For (gar) is a marker of cause or reason positioned after a preceding clause and introducing the reason or cause for what has just been stated) looks at the last clause of Ro 2:12-note and explains why the Jews shall be judged by the Law.

Mere knowledge of the Law ("hearers") will not satisfy divine justice for it is not the hearers, but the doers, that are justified (cf Jas 1:22-note). God’s righteous judgment is not withheld because someone has heard the Law; it is only held back if someone has "done" the Law.

The Jew may think that he is saved because he has the Law; but Paul is saying that the question he needs to address "Have I kept the Law?" The Jews may have possessed the Law but they did not practice the Law. And of course no man can "practice the law" unless they are given a divine "heart transplant" which is exactly what Paul is building up to in his indictment of everyone still in Adam and dead in their trespasses and sins. In a similar manner, a Gentile might suppose that he is saved because he has kept the dictates of his own conscience. Paul is arguing logically that clearly this is not possible.

Both groups

will be condemned, not because they have the Law or do not have the Law, but because they have sinned. (Morris)

Hearers (202) (akroates from the verb akouo = hear with attention) describes those who of those who sat passively in an audience and listened to a singer or speaker.

Vincent writes that "hearers" are those...

Like the Jews...heard it regularly in the synagogues. (Akroates is found) Only here in Paul. Three times in James. It brings out, better than the participle hoi akouontes those that hear, the characteristic feature; those whose business is hearing.

Jews attended their synagogues, week after week hearing the law read and explained to them. They were professional hearers but should have been proficient doers! (cf Jas 1:22-note)

MacArthur adds this helpful note

Paul here does not use the usual Greek term for hearing (akouo) but the word akroates, which was used of those whose business it is to listen. The idea is much like that of a college student. His primary purpose in class is to listen to the teacher’s instruction. Normally, he also has the responsibility of being accountable for what he hears and is tested on it. If he is simply auditing, however, he is required only to attend the class sessions. He takes no tests and receives no grade. In other words, he listens without being held accountable for what he hears. In many synagogues during Paul’s time, teaching did not focus on Scripture but on the system of man-made traditions that the rabbis had developed over the centuries since the Exile. Frequently, God’s Word in the OT was merely read and listened to, without explanation or application. Most Jews, therefore, were simply “auditing the course,” hearers of the Law and nothing more. But God recognizes no mere “auditors” of His Word. The more a person hears His truth, the more he is responsible for believing and obeying it. Unless there is obedience, the greater the hearing, the greater the judgment."

Just (dikaios) is an adjective which describes the man who is in accordance with what God requires. God is totally righteous because He is totally as He should be. The righteousness of God which He requires is all that God is, all that He commands, all that He demands, all that He approves and ultimately all that He provides (through Christ).

Note that "not" is the Greek word "ou" which signifies absolute negation of what follows. Paul is saying that merely "hearing" the Law justifies absolutely no one. The Jew boasted in knowing the Law, but Christ said, "None of you keep the Law." Applying this passage to the modern church, in the opinion of many evangelical pastors there are many individuals who upon hearing the gospel preached have made an outward "profession" but whose lives fail to exhibit fruit in keeping with genuine repentance (Mt 3:8) or good works (Eph 2:10-note) that indicate that they have been truly born again.

BUT THE DOERS OF THE LAW WILL BE JUSTIFIED: all hoi poietai nomou dikaiothesontai (3PFPI): (Ro 3:20,23; 10:5; Lk 10:25, 26, 27, 28, 29; Gal 3:11,12) (Doers Mt 7:21; 12:50; Lk 11:28; 2Co8:11; Jas 1:22, 23, 24, 25, 26, 27; 4:11) (justified Ro 3:30; 4:2, 3, 4, 5; Ps 143:2; Lk 18:14; Acts 13:39; Gal 2:16; 5:4; James 2:21, 22, 23, 24, 25-see notes) (See Torrey's Topic Justification before God, see articles in ISBE Easton)

Justified (1344) (dikaioo from dike = right, expected behavior or conformity, not according to one’s own standard, but according to an imposed standard with prescribed punishment for nonconformity) (Click more discussion of dikaioo) primarily means to deem to be right.

The Law demands perfect and continuous obedience for one to be "justified". Paul has clearly stated that no one is accounted righteous simply because he hears or knows what the Law says. The only conceivable way of being justified under the Law would be to keep it in its entirety. But since all men are sinners, it is impossible for them to do this. So this verse is really setting forth an ideal condition rather than stating something that is capable of human attainment.

Constable comments that...

It is not hearing the law that makes a person acceptable to God, but doing what it commands (Ro 2:13). “Justified” is a legal term that is suitable in this discussion of law observance. Justification is a legal verdict. It reflects a person’s position under the law. The justified person is one whom God sees as righteous in relation to His law (cf. Dt 25:1). The justified person is not necessarily blameless; he may have done things that are wrong. Nevertheless in the eyes of the law he is not culpable. He does not have to pay for his crimes. Paul said in Ro 2:13 that God would declare righteous the person who did not just listen to the Mosaic Law but did what it required. The Law warned that anything short of perfect obedience to it, even reading or studying it or hearing it preached and taught, which Jews relied on, made a person guilty before God (Dt 27:26; cf. Ga 3:10). Moses therefore urged the Israelites to accept and believe in the promised Messiah (e.g., Deut 18:15). (Constable's Expository Notes on the Bible) (Bolding added)

Paul will bring the truth about justification to fruition in Romans 3. In this chapter he is making it clear that no man in his own strength cab be justified before God.

MacDonald has a nice summary of this section

"The NT teaches emphatically that it is impossible for man to be justified by law-keeping (Acts 13:39; Ro 3:20-note; Gal 2:16, 21; 3:11). It was never God’s intention that anyone be saved by the law. Even if a person could keep it perfectly from this day forward, he still would not be justified, because God requires that which is past. So when verse 13 says that doers of the law will be justified, we must understand it as meaning that the law demands obedience, and if anyone could produce perfect obedience from the day he was born, he would be justified. But the cold, hard fact is that no one can produce this." (MacDonald, W., & Farstad, A. Believer's Bible Commentary : Old and New Testaments. Nashville: Thomas Nelson)

William Newell writes

"Yet it is deeply instructive here to quote a passage like that of [Lu 1:6], concerning Zacharias and Elizabeth: "They were both righteous in the sight of God, walking blamelessly in all the commandments and requirements of the Lord." Now their walk was not the ground of their acceptance (Ed note: but is was the fruit of their faith), although only such as they are accepted! For they were subject to God’s Word, not mere hearers, but doers. (Ed note: again the only way Zacharias & Elizabeth could have been righteous "doers" is because they had at some point in time believed God's promises concerning the Messiah and God had reckoned their faith to them as righteousness [cf Ro 4:5-note] Luke does not tell us when they believed but from Romans & Galatians there is no other way they could have been declared righteous). The first verse of the book of Job (Job 1:1) describes another such person. Indeed, at heart all God’s saints are such."  (Romans 2)

Newell's point is that genuine saving faith results in a declaration of their righteousness and a consequent obedient and godly lifestyle, even though punctuated with fleshly failure from time to time. When God measured the deeds of the Jews, He found them to be as wicked as those of the Gentiles. The fact that the Jews occasionally celebrated a feast or a Sabbath did not change the fact that their consistent daily life was one of disobedience to God and to His perfect Law. God’s blessings did not lead them to repentance. The majority of them heard the Law but did not do the Law (the righteous remnant like Zacharias and Elizabeth being exceptions) and so were not justified or declared righteous (in right standing) before God.

Torrey's Topic
Justification Before God

For (gar) is a marker of cause or reason positioned after a preceding clause and introducing the reason or cause for what has just been stated) and here looks back not to Ro 2:13 but to Ro 2:12. Paul is explaining that the Gentiles also have a law so to speak by which they will be judged. Paul explains in this section that the Gentiles can be condemned without the law because their conscience (which is the work of the law written in their hearts) is enough to condemn them. As testimony to the truth of this principle, it is interesting to note that many of the unsaved pagan writers of  Paul’s day referred to the "unwritten law" within man. Even these pagans recognized that there was something instinctively present within a man or a woman which tries to direct us in the right way. Remember that although all men are totally depraved in the sense that they cannot do anything that is righteously good, they can do a "man kind of good" like honoring their parents, paying their debts, etc. But every time they do that they prove that there is a law within them that points to that as good. Are they lost? Yes. Can they claim ignorance? No. As Paul pointed out in Romans 1, creation is around them proclaiming that God exists. In Romans 2 Paul is piling up the evidence against them, showing that by their conduct they prove that they have an inner moral law.

Stedman writes:

"Now, men are continually charging God with injustice because, they say, He condemns men to hell who have never heard of Jesus Christ. This is the most frequently voiced charge against the Christian gospel. We are always hearing somebody say, "Well, what about the heathen who never hear about Christ? How can a just God condemn them to hell without their hearing about Christ?" But, you see, God never condemns anybody on that basis. As we are told right here...That is, if you disobey the truth that you have, even though you have never heard of Moses or of Christ, you perish, not because you didn't hear of Moses or of Christ, but because you have disobeyed truth that you already know -- that is the whole point. If you know of Moses and of Christ, and you still disobey the truth, you perish also, because your condemnation is even greater -- because of the greater light involved. (Ed note: See above for discussion of the principle of judgment proportionate to light received) But, as it says here, even pagans have a form of basic law written on their hearts, and this is the basis of God's just condemnation of man. It is because they are not what they themselves know they ought to be. In other words, God judges you, not by some artificial standard of His, but by your own standard."

Stedman goes on to give an illustration of Paul's point:

"Recently, I was down in Newport Beach, teaching a Bible Class in a home. Quite a number of non-Christians were there, and one of them was a man from just across the street. He was a very charming individual, but he had made it known in the neighborhood already that he had no use for Christianity. As he came in the door, the first thing he said was, "I have come to be the Devil's advocate. I think the Devil needs a representative here tonight." We welcomed him, and told him to curl his tail around a chair, and sit down. As I began to speak on the opening chapter of Genesis, dealing with God's word to man, I could see in his face that this man had let down his guard. I don't think he was aware of how much he was revealing, but in that man's eyes I saw hunger written like I had never seen it before. At the question time, he, of course, came up with the usual question : "How about those that God condemns who never hear about Christ?" I answered (to all in the room), "Let me ask you this: Which of you has lived up to your own ideals? -- because God won't judge you on the basis of something that you have never heard, but on the basis of what you already know. Now tell me: Who of you has lived up to his own ideals? Which of you has never deliberately done wrong? Which of you can say that you measure up to your own standard of what you ought to be?" You could just hear the silence in that room! You see, it is not by some artificial standard that we stand condemned before God; it is because of what we know in our hearts about ourselves. This indicates that God measures us by our own yardstick." (Romans 2:1-16 The Secrets of Men)

GENTILES WHO DO NOT HAVE THE LAW DO INSTINCTIVELY THE THINGS OF THE LAW: ethne ta me nomon echonta (PAPNPN) phusei ta tou nomou poiosin (3SPAS): (Ro 2:12; 3:1,2; Dt 4:7; Ps 147:19,20; Acts 14:16; 17:30; Ep 2:12) (do Ro 2:27; 1:19,20; 1Co 11:14; Php 4:8) (See Greek/Gentile in Easton, Smith, ISBE, Torrey's Topical)

Without knowing the written law of God, men and women in pagan societies by nature, instinctively value and attempt to practice justice, honesty, compassion, goodness toward others, etc, this practice testifying to the fact that the divine law has been written in the heart of even the most primitive tribesman. While Paul says that a Gentile may by nature do the things contained in the law, he is very careful not to say that a Gentile could fulfill the requirements of the law by nature.

THESE, NOT HAVING THE LAW, ARE A LAW TO THEMSELVES: houtoi nomon me echontes (PAPMPN) heautois eisin (3PPAI) nomos:

"The Gentiles do not have the Law; but whenever they do by instinct what the Law commands, they are their own law, even though they do not have the Law" (TEV),

"Even when Gentiles, who do not have God's written law, instinctively follow what the law says, they show that in their hearts they know right from wrong." (NLT)

"For example, whenever non-Jews who don't have laws from God do by nature the things that Moses' Teachings contain, they are a law to themselves even though they don't have any laws from God." (GWT)

The Gentile's practice of some good deeds and their aversion to some evil ones demonstrate an innate knowledge of God’s law and this knowledge will actually witness against them on the day of judgment.

John Calvin adds that here Paul

shows that ignorance is in vain pretended as an excuse by the Gentiles, since they prove by their own deeds that they have some rule of righteousness.

To reiterate, Paul is simply saying that God has written on the heart of every man a basic moral code. That code is similar to the things contained in the Ten Commandments. This universal moral code consists of things like "Do not steal," "Do not cheat," "Tell the truth," "Honor your parents," "Keep your word," "Help the poor," "Do not kill," etc. It would be hard to find a culture anywhere in the world where those moral values are not honored.  The Greek poet Sophocles spoke of "the unwritten and indelible laws of the gods." The Platonic philosopher Plutarch called it "a law which is not written in books, but implanted in the heart of man." In fact, this concept of a universal moral code was widely discussed by the Greeks and Romans. Paul simply picks up that concept and applies it to the Gentiles.

Don't misunderstand what Paul is saying with the phrase "a law to themselves". He is not implying that these "obedient Gentiles" made up their own law (as we often use the expression in modern parlance describing a rebel as a "law unto himself"), but that they were obedient to conscience, the work of the law residing in themselves.

Note also that while Paul that a Gentile, may, by nature do the things contained in the law; he does not say that a Gentile could fulfill the requirements of the law by nature.

One other thought to keep in mind when reading Paul is that the word “Law” can be confusing, and can refer to the Pentateuch, to the entire Old Testament, to the Ten Commandments, to the whole body of God’s requirements for Israel, and to the way of life adopted by the covenant community. In Romans 2-3 the basic meaning of “law” is “God’s revealed requirements for righteous living.”

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Dirty Hands - One of William Shakespeare’s most intriguing characters is Lady Macbeth. Having heard a prophecy that her husband would become king, she convinced him to assassinate the reigning monarch. When the bloody deed was done, Macbeth was conscience-stricken. His wife rebuked his squeamishness and helped him cover up the crime. Her husband was crowned king. But that wasn’t the end.

Lady Macbeth’s initial resolve turned to remorse. She grew mentally unstable, and couldn’t stop washing her hands. “Will these hands ne’er be clean?” she asked. Finally, the guilt drove Lady Macbeth to suicide.

Guilt is an emotion that can weigh us down whenever we cross a moral boundary. All of us are capable of feeling guilty when we violate the law of God written in our hearts (Romans 2:14, 15). If we continue to sin willfully, however, we will dull our conscience.

Lady Macbeth is a good reminder of a biblical principle: Whatever we sow, we will certainly reap (Galatians 6:7, 8). When we feel temptation, we need to listen to our conscience—not try to silence it. It’s far better to avoid committing an act we will later regret than to live with the consequences. —Dennis Fisher (Our Daily Bread, Copyright RBC Ministries, Grand Rapids, MI. Reprinted by permission. All rights reserved)

Sometimes there’s just one step to go
Before we yield to sin,
But God will help us to say no
If we trust His power within. —Hess

IN THAT THEY SHOW THE WORK OF THE LAW WRITTEN IN THEIR HEARTS: hoitines endeiknuntai (3PPMI) to ergon tou nomou graphton en tais kardiais auton: (Ro 1:18, 19- notes)

Show (1731) (endeiknumi from en = in, to + deíknumi = show)

Showing (1731) (endeíknumi [word study] from en = in, to + deíknumi = explain meaning or significance of something by demonstration) means to indicate by word or act.  The idea is to show forth, demonstrate, prove, whether by arguments or acts.

Heart (2588) (kardia) does not refer to the physical organ but is always used figuratively in Scripture to refer to the seat and center of human life. It represents the inner person, the seat of motives and attitudes, the center of personality. In Scripture kardia is much more than emotion or feelings, but includes the thinking process and particularly the will.

Barclay commenting on the "Work of the Law" writes that...

We would call it the instinctive knowledge of right and wrong. The Stoics said that in the universe there were certain laws operative which a man broke at his peril—the laws of health, the moral laws which govern life and living. The Stoics called these laws phusis, which means nature, and urged men to live kata phusin, according to nature. It is Paul’s argument that in the very nature of man there is an instinctive knowledge of what he ought to do. The Greeks would have agreed with that. (Barclay, W: The Daily Study Bible Series, Rev. ed. Philadelphia: The Westminster Press)

People who have never heard God's word directly still have a moral compass that they are accountable to. E.g., all men know it is wrong to lie, steal, and murder.  Mankind recognizes that there is a code of ethics. In fact man has a guilty conscience because he violates that very code of ethics within him.

William Newell  (Romans 2) asked Chinese who had never heard the Law or the gospel if they knew these things were wrong; they all admitted they did. Even those persons who have never heard of the Bible have still been preached to with sufficient clarity (God has made it evident within them - Ro 1:19-note, as well as without - Ro 1:20-note) to remove every excuse from their hearts forever. He is not- saying that the Law of Moses is written on their hearts, as people often say, but that the work of the law, i.e., what the law requires of people, is written there.

MacArthur makes an interesting observation noting that...

The fact that such people did good things, knowing they were ethically good, proves they had knowledge of God’s Law written in their hearts. Therefore if those people never come to trust in the true God, their good deeds will actually witness against them on the day of judgment. (MacArthur, J: Romans 1-8. Moody)

Unregenerate people do relative human good, but they don't do good in terms of spiritual righteousness. Their good is not based on the right motive because nothing is truly good unless it is done for the glory of God. But they do good in a relative human sense. When they do that they show the law of God at work in them. They do good in the right manner if not for the right motive. (Romans 2-11-16 Principles of God's Judgment)

Thus Paul explains why the Gentile can be condemned without the law...how it is that God is fair in condemning those who have never even had a Bible. Paul clearly demonstrates that their conscience (the work of the law written in their hearts) is enough to condemn. Many pagan authors of Paul's day referred to the "unwritten law" within man; something which points us to the right way.

People who have never heard God’s word directly still have a moral compass that they are accountable to.

"God is describing how He has constituted all men: there is a ‘work’ within them, making them morally conscious." (William Newell) "  (Romans 2)

Morris observes that Paul...

"...is not saying that the law is written on their hearts, as people often say, but that the work of the law, what the law requires of people, is written there."

THEIR CONSCIENCE: auton tes suneideseos: (Romans 9:1-note; John 8:9; Acts 23:1; 24:16; 2Corinthians 1:12; 5:11; 1Timothy 4:2; Titus 1:15-note) (Click  2Timothy Notes or Titus Notes for more on "conscience") (Torrey's Topic Conscience, Nave's Topic Conscience; see also Easton, ISBE)

Conscience (4893)  (suneidesis [word study] from sun = with + oida = know) means literally "a knowing with" or a co-knowledge (with oneself) and represents the witness borne to one's conduct by one's own indwelling, instinctive sense of right and wrong that produces guilt when violated  ("alternately accusing"). 

Suneidesis - 30x in 29v - Acts 23:1; 24:16; Rom 2:15; 9:1; 13:5; 1 Cor 8:7, 10, 12; 10:25, 27ff; 2 Cor 1:12; 4:2; 5:11; 1 Tim 1:5, 19; 3:9; 4:2; 2 Tim 1:3; Titus 1:15; Heb 9:9, 14; 10:2, 22; 13:18; 1 Pet 2:19; 3:16, 21

Conscience has been succinctly described as the

soul distinguishing between what is morally good and bad, prompting to do the former and shun the latter. 

In addition to an innate awareness of God’s law, men have a warning system that activates when they choose to ignore or disobey that law. It's that  instinctive, built-in sense of right and wrong that activates guilt.

All mankind has an innate inner sense of right and wrong which Scripture refers to as conscience. And so sociologist have encountered in all cultures a sense of sin and fear of judgment which leads that culture to make some attempt to appease whatever gods are feared and this built in "moral/ethical radar detector" (so to speak) is what Paul is alluding to here in Romans 2.

Conscience is like an inner judge that accuses and condemns us when we have done wrong and approves and commends us when we have done right. The conscience varies in sensitivity, depending on the degree of one’s knowledge of and feeling about right and wrong. The person who has considerable knowledge of God’s Word will have a more sensitive conscience than someone who has never had opportunity to know Scripture. Furthermore, repeated sinning hardens the conscience so that it becomes “seared” like scar tissue (1Ti 4:2). To continually reject God’s truth causes the conscience to become progressively calloused, hardened and less sensitive to sin, as if covered with layers of unspiritual scar tissue. There is an interesting parallel in tropical medicine which has discovered that the gross disfigurement so commonly seen in individuals with leprosy is not due to the leprosy bacterium per se, but is secondary to the organism's destruction of the nerve fibers that convey a sense of pain and touch. Unprotected by the body's natural warning signals the leper repeatedly injures the extremity with cuts, burns, infections, etc, all without even realizing that he is injured! This is exactly the picture of the seared conscience which becomes insensitive to sin and may eventually cease sending warning signals. Thus, though God has His work within every man resulting in conscience, man can corrupt that work, so that the "sin sensitivity" rating of the conscience varies from person to person.

Ray Stedman has some interesting thoughts on conscience writing that...

We each have a conscience. We may not be able to analyze it, and we certainly cannot control it, but we know we all possess one. Conscience has been defined as "that still, small voice that makes you feel smaller still," or, as one little boy put it, "It is that which feels bad when everything else feels good." Conscience is that internal voice that sits in judgment over our will. There is a very common myth abroad that says that conscience is the means by which we tell what is right and what is wrong. But conscience is never that. It is training that tells us what is right or wrong. But when we know what is right or wrong, it is our conscience that insists that we do what we think is right and avoid what we think is wrong. That distinction is very important and needs to be made clear.

Conscience can be very mistaken; it is not a safe guide by itself. It accuses us when we violate whatever moral standard we may have, but that moral standard may be quite wrong when viewed in the light of God's revelation. But conscience also gives approval whenever we fulfill whatever standard we have, though that standard is right or wrong. And conscience, we have all discovered, acts both before and after the fact -- it can either prod or punish. (A Clear Conscience)

Franklin P. Jones wrote that

"Conscience is a small, still voice that makes minority reports."

Someone added

"Conscience is also what makes a boy tell his mother before his sister does."

Christopher Morley said about conscience

Pop used to say about the Presbyterians, 'It don't prevent them committing all the sins there are, but it keeps them from getting any fun but of it.'

The late General Omar Bradley was more serious in commenting on conscience

"The world has achieved brilliance without conscience," he conceded. "Ours is a world of nuclear giants and ethical infants."

On the subject of conscience Martin Luther declared before the court of the Roman Empire at Worms in 1521

"My conscience is captive to the Word of God. ... I am more afraid of my own heart than of the pope and all his cardinals. I have within me the great pope, Self."

When a person comes to faith in Christ, his conscience becomes acutely sensitive to sin. No longer as a Christian can he sin with impunity. The story is told about an old Indian chief who was converted. Later a missionary asked him:

"Chief, how are you doing spiritually? Are you experiencing victory over the devil?"

"It's like this," the chief replied. "I have two dogs inside me: a good dog and a bad dog. They are constantly fighting with each other."

"Which dog wins?" asked the puzzled missionary.

"Whichever one I feed the most," retorted the wise old man. His conscience was being shaped by the Scriptures.

Billy Graham set out the importance of a clear conscience

"To have a guilty conscience is a feeling. Psychologists may define it as a guilt complex, and may seek to rationalize away the sense of guilt, but once it has been awakened through the application of the law of God, no explanation will quiet the insistent voice of conscience."

MacArthur recounts an interesting illustration of the human conscience:

It is reported that a tribe in Africa had an unusual but effective way to test the guilt of an accused person. A group of suspects would be lined up and the tongue of each would be touched with a hot knife. If saliva was on the tongue the blade would sizzle but cause little pain. But if the tongue was dry, the blade would stick and create a vicious, searing burn. The tribe knew that a sense of guilt tends to make a person’s mouth dry, and a seared tongue therefore was taken as proof of guilt. The making of such a dry mouth is, of course, the work of the conscience. (MacArthur, J: Romans 1-8. Chicago: Moody Press or Logos)

Pritchard offers a hypothetical illustration:

"This week I read an ancient tale about a court magician who wanted to give his king a very special gift. After much work, he designed a magic ring which had a very special property. Every time the king had an evil thought or an unworthy ambition, the ring began to shrink tightly around his finger, thus warning him of impending danger. The human conscience is like that. It is a ring around the heart, which tightens every time we begin to violate our own standards. It warns of impending danger. We disregard our conscience at our own peril. And, Paul says, every man has a conscience, a "ring around the heart." No one can say, "I've never done wrong," because every man has violated his conscience at least once, and most of us many times. That's why God can fairly judge the Gentiles. The law "written in their hearts" will be the standard by which they will be judged. Their guilty consciences will one day rise up to condemn them."

A W Tozer says that

"Conscience singles you out as though nobody else existed. God has given us a faithful witness inside of our own being...It is able to single a man out and reveal his loneliness, the loneliness of a single soul in the universe going on to meet an angry God. That’s the terror of the conscience. Conscience never deals with theories. Conscience always deals with right and wrong and the relation of the individual to that which is right or wrong. Remember the conscience is always on God’s side! It judges conduct in the light of the moral law, and as the Scripture says, excuses or accuses."

Barclay gives an interesting historical perspective on "conscience" referring to it as...

the instinctive knowledge of right and wrong. The Stoics said that in the universe there were certain laws operative which a man broke at his peril—the laws of health, the moral laws which govern life and living. The Stoics called these laws phusis, which means nature, and urged men to live kata phusin, "according to nature". It is Paul’s argument that in the very nature of man there is an instinctive knowledge of what he ought to do. The Greeks would have agreed with that. Aristotle said: “The cultivated and free-minded man will so behave as being a law to himself.” Plutarch asks: “Who shall govern the governor?” And he answers: “Law, the king of all mortals and immortals...which is not written on papyrus rolls or wooden tablets, but is his own reason within the soul, which perpetually dwells with him and guards him and never leaves his soul bereft of leadership."  (Barclay, W: The Daily Study Bible Series. The Westminster Press or Logos)

Unless of course it becomes seared as did the "inner moral compass" of the Roman Emperor Nero, whose evil exploits are too despicable to even be reviewed in these notes.

Thomas Brooks wrote that...

Conscience is God's deputy, God's spy, God's notary, God's viceroy...Conscience is God's preacher in the bosom.

BEARING WITNESS: summarturouses (PAPFSG):  

Bearing witness (4828) (summartureo from sún = together, with, + marturéo = to witness) means to witness with another or to testify with. This verb was used in the Greek secular writings where the signature of each attesting witness is accompanied by the words "I bear witness with and I seal with". The present tense indicates this activity was continuous.

Mark Twain quipped that you can tell if something you did was morally good if you "felt good afterward." But if it left you "feeling bad," it was morally wrong. This statement can be understood in two ways. One is that good or bad conduct can produce good or bad feelings. This is true. The other is that feelings determine what is good or bad. A secular writer showed the fallacy of this interpretation when he said, with tongue in cheek, that he liked Twain's statement because it implied that you've got to try something at least once to know whether it's good or bad.

Beware that feelings are not a reliable indicator of moral conduct. The only trustworthy standard is God's Holy Inerrant Fully Sufficient Word. To obey the Lord's commands sometimes goes against our emotions (or feelings). To forgive others, for example, isn't our natural tendency. Yet we know that is what God wants us to do. And when you've either forgiven someone or sought forgiveness, haven't you experienced an inner relief and release after obeying your conscience? Sure you have.

AND THEIR THOUGHTS ALTERNATIVELY ACCUSING OR ELSE DEFENDING THEM: kai metaxu allelon ton logismon kategorounton (PAPMPG) e kai apologoumenon (PMPMPG): (Genesis 3:8, 9, 10, 11; 20:5; 42:21,22; 1Kings 2:44; Job 27:6; Ecclesiastes 7:22; 1John 3:19, 20, 21)

Based on their instinctive knowledge of right and wrong that comes from their conscience, unbelievers still possess the ability to determine things as basically right or wrong. In each unregenerate person is the ability to contemplate or reason what someone does as right or wrong. For example, a person without Christ hears about someone who murdered a child. What is his reaction? Unless he's completely given over to evil, he's going to accuse the murderer.

Another way to look at this verse is to note that whether unbelievers kept or broke these natural laws determined whether their thoughts acquitted or condemned them.

That unbelievers could know enough to do right some of the time renders them without excuse for ever doing wrong.

What Paul is saying is that the pagan's conscience is like a witness in a courtroom who takes the stand and provides unquestionable testimony against him that he actually knew what he did was wrong.

Here is an excellent summary of Romans 2:14, 15 from  (Middletown Bible Church)...

The Gentiles do not have the written law of God. They do not have the law of Moses. But according to these verses they have God’s law WITHIN THEM, "written in their hearts." Although they have never seen a copy of the Ten Commandments, they know that it is wrong to murder, steal, lie, etc. And their conscience condemns them when they do such things. Here are two examples:

1) Acts 28:3,4. These barbarians never saw the Ten Commandments but somehow they knew that murder was wrong and that it was punishable by death!

2) Genesis 26:6, 7, 8, 9, 10, 11. This heathen king had never seen the Ten Commandments yet he knew that adultery was wrong.

"Accusing" = "You’re guilty! What you did is wrong!"
"Excusing" = "You’re not guilty! What you did is right!"

When they do RIGHT their conscience applauds and cheers. When they do WRONG their conscience condemns them and says "You are guilty!"

Thus, the Jew sinned by failing to do what the law of Moses commanded him to do. The Gentile sinned by failing to do what his conscience told him to do. Both Jew and Gentile failed to live up to the light God had given. Both are condemned before God. (Middletown Bible Church)

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A Cleansed Conscience - The much-loved children's story Pinocchio is about a wooden puppet whose nose grows long when he tells a lie. His friend Jiminy Cricket chirps, "Let your conscience be your guide." Pinocchio follows his advice, repents, and returns to Geppetto his creator, where he is given a heart of flesh and is freed from his strings.

There's a principle in this story for God's children. If we don't listen to that voice deep down inside that tells us what we should and should not do, we live in bondage. But a cleansed conscience brings freedom.

Some people have no strong basis for making godly decisions. Their conscience is weak, and they can be easily swayed by the behavior of others. Then there are those whose conscience is defiled. The standard by which they measure good and evil is corrupted, polluted, and impure (Titus 1:15-note). But saddest of all are those who have a "seared" conscience (1Timothy 4:2). They have resisted that inner voice for so long that they no longer hear what it has to say.

But you ask, "How can we have a cleansed conscience?" We must repent of our sin and return to our Creator. We must ask Him to conform our desires and behavior to His Word and then be careful to obey it. —David Roper  (Our Daily Bread, Copyright RBC Ministries, Grand Rapids, MI. Reprinted by permission. All rights reserved)

There is a treasure you can own
That's greater than a crown or throne;
This treasure is a conscience clear
That brings the sweetest peace and cheer.
—Isenhour

Conscience is a trustworthy compass
when God's Word is your true north.

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THE WITNESS OF CONSCIENCE (F B Meyer, Our Daily Walk)

Sometimes we can meet ourselves with a smile; this is what we term a good conscience; at other times we do not like to meet ourselves, but feel ashamed--we cannot deceive ourselves, or hoodwink conscience. We know, and we know that we know, that this is right and that wrong; this is good, and that evil. Conscience is an ill bed-fellow, says the old proverb, and when we are troubled with evil dreams, turning, tossing, starting up in fear, rest becomes impossible. It is very necessary to keep on good terms with your conscience, and we do not wonder that the Apostle made it his aim to preserve a conscience void of offence towards God and man (Act 24:16).

All men have a conscience, else God could not judge them; there would be no standard by which to try or convict, but in most cases conscience is uninstructed. It judges rightly, so far as it knows, but its knowledge is scant, and its power of making accurate distinctions is limited. The Christian conscience is illumined and instructed by the light that falls on it from the face of Christ. See to it that your conscience is constantly corrected by Christ's standard. Never tamper with conscience, nor gag her protestations, nor drown her voice. Never say it does not matter for once in a way. Never dare to let her voice wear itself out. To behave thus is to tamper with the most delicate moral machinery in the universe. Let us see that our hearts are sprinkled from an evil conscience in the blood of Jesus, so that we may draw near with a true heart in full assurance of faith (Heb 10:19, 20, 21, 22, 23-note).

PRAYER: O Lord, give me Thy Holy Spirit in greater measure, that His saving presence may cleanse my conscience, and His holy inspiration enlighten my heart. AMEN.

This is a great announcement, and shows how God can judge men who have never heard of the Bible or the Decalogue. The latter is engraven on their hearts, and is witnessed to by conscience.

Conscience is an original faculty. We are no more called upon to investigate its origin than the mathematician to inquire how the mind can add, or multiply, or divide; or than the artist to ask why we can appreciate the beautiful. It is part of the make-up and constitution of our moral nature. The word ought lies behind conscience, investing it with the certainty and irresistibleness of the throne of God.

Conscience is the judgment-seat of God set up within our nature. You may always know when conscience speaks. She never hesitates, or questions, or pronounces on the expediency of a course; but, as any case is presented to her, she pronounces absolutely and directly upon it as right or wrong. And as she speaks, she anticipates the verdict of the great white throne.

ON THE DAY WHEN ACCORDING TO MY GOSPEL: en hemera hote kata to euaggelion mou:  (my gospel - Ro 16:25-note; 1Ti 1:11; 2Ti 2:8-note) (Torrey's Topic Gospel)

On that day-  the day of judgment.

Spurgeon describes it as follows:

"A judgment is going on daily. God is continually holding court, and considering the doings of the sons of men. Every evil deed that they do is recorded in the register of doom, and each good action is remembered and laid up in store by God. That judgment is reflected in a measure in the consciences of men. Those who know the gospel, and those who know it not, alike, have a certain measure of light, by which they know right from wrong; their consciences all the while accusing or else excusing them. This session of the heavenly court continues from day to day, like that of our local magistrates; but this does not prevent but rather necessitates the holding of an ultimate great assize (verdict rendered).

Saints (saved sinners) will stand at the Judgment seat (bema - see note) of Christ and unsaved sinners at the Great White Throne judgment (described in Rev 20:11, 12, 13, 14,15-note) and all be be judged according to "my gospel." On the day when God will judge the secrets of men, no man can find refuge from God’s judgment by claiming ignorance of His written revelation for violation of God’s internal revelation is enough to condemn us all. Notice that the day of judgment was a part of Paul's gospel and he did not shrink from declaring man's absolute accountability to God.

Vincent comments that the expression, “my gospel”  distinguished Paul's message 

“from false teaching. Paul’s assurance of the truth of the gospel is shown in his confident assertion that it will form the standard of judgment in the great day.” Cranfield interprets this phrase more generally as “My gospel declares that the judge will be Christ Jesus”

Spurgeon adds that

"My gospel" saith he, with a rapture of delight, as he presses to his bosom the sacred deposit of truth.  "My gospel" Does not this show his courage? As much as to say, "I am not ashamed of the gospel of Christ: for it is the power of God unto salvation to every one that believeth." He says, "My gospel" as a soldier speaks of "my colors," or of "my king." He resolves to bear this banner to victory, and to serve this royal truth even to the death. "My gospel" There is a touch of discrimination about the expression. Paul perceives that there are other gospels, and he makes short work with them, for he saith, "Though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let me be accused." (Gal 1:6ff)

Pastor Ray Stedman writes some sobering, convicting words at the conclusion of his message entitled "The Secrets of Men":

"Christ will be the judge, we are told. The gospel will be the prosecuting attorney. The charge will be the secrets of the heart that no one knows about but you -- and God. Samuel Johnson once said, "Every man knows thoughts of himself that he would not tell to his dearest friend." That is true, isn't it? And you know it is not so much the thoughts that come to our mind, because these are often temptations we are powerless to stop, but it is the reception we give them. We sometimes open the door and welcome them, don't we? Instead of driving these thoughts away when they come, we usher them into our living room, and set them down, and ask them to be comfortable and stay with us, and we invite them back again and again; we allow them to dwell there. These are the secret things that we don't want to tell anybody about -- even our dearest friend. Let me tell you part of the secrets of my own heart, if I may. I catch myself, every now and then (and I have for years), trying to figure out a way to perform a certain sin (which is particularly alluring to me) without paying the consequences. Don't look so shocked, because you do the same thing! I have worked out many ingenious ways by which I can make it "look good" to men, so nobody will blame me if I do this. It is amazing, the variety of ways that a matter can be approached to make it look acceptable to others. But the thing that stops me dead in my tracks is that, though I know I can make it look good to others, God knows my evil heart. And, someday, the thing that I can make look good to men will be seen in all its filth and depravity in his sight, and I will have to acknowledge that this is what it was all the time. Because I know that God knows the secrets of my heart, I am continually checked on this thing.

Now, this the ministry of the Spirit in our lives. Jesus spoke of the day when that which is uttered in secret shall be shouted from the housetops {cf Lk 8:17} -- and God knows our hearts now, but he will judge them then. I was in a class last week talking about Noah and the flood. What a wonderful story that is! What a remarkable man Noah was! And, really, the only difference between Noah and the others of his day was that Noah made room in his life for God. That is all. It's wonderful to notice that. This man walked with God, and talked with God about everything in his life -- all the little things and all the big things. And, for 120 years, as the ark was being built, God talked to him about the details of that ark as they went over the blueprints together. God would tell him were to put the window, and the door, and so on, as they worked and walked together.

Now, we read that Noah was a righteous man, but he didn't make himself righteous and then go looking for God. He just let God in, and God made him righteous. (cf Heb 11:7-note) That is the whole secret. But then the flood came. Suddenly the delicate balance of nature was tipped by the evil of man, and the violence that was in the earth. The flood began to form. "The windows of heaven were opened," {Ge 7:11KJV}, "the fountains of the great deep" were opened; the waters began to rise. Calamity came upon the world of Noah's day, but Noah was safe in the ark -- where God had shut him in. And I said to the people of the class, "This is exactly what everyone in the room faces!" And this is true for all of us. Every one of us lives in exactly the same relationship in which the people of Noah's day lived. There is a great calamity coming, that we cannot escape, that will sweep away everything we have. It is as certain and sure as tomorrow morning's sun. It is what we call "death." When it strikes, it will be too late to build an ark. But God is talking to us; God is trying to reach us; God is dealing with us. God is trying to break into our lives in order that we might begin building our ark now. It was really God who built Noah's Ark, not Noah. Noah just obeyed what God told him. God built the ark, and, in the moment of disaster, it was a place of safety for Noah. Now, this is what our Lord is telling us he doing today.

Why does God tell you this that is recorded here in Romans 2? Is it because he wants you to despair? Is it because he wants you to realize that, when you stand before him, there is no chance? Obviously that is true, isn't it? We have no chance of standing in God's sight on our own merits. Is anyone prepared to stand up, and say, "If God is going to deal with me on this basis, I am prepared to meet him on these terms"? Of course not, all of us know we don't have a ghost of a chance. But does God tell us this to torment us? Of course not! He tells us this in order that we might give serious considerations to the gospel of his Son, Jesus Christ, because, in that gospel, God has made a way by which he can offer us righteousness which is perfectly acceptable in his sight -- a righteousness that we have nothing to do with ourselves, but which has been obtained for us by the work of another. In the gospel there is a way by which we may stand before God -- perfectly acceptable to him, without any doubt, without any possibility of failure. Now, that is why God tells us the truth about ourselves. I watched the faces of the men during those recent breakfast meetings and saw them listening to men like themselves tell how they became aware of the great, empty vacuum in their lives, and how Christ came in and filled their lives. Some of these were men who had not given serious consideration to the claims of Jesus Christ perhaps for years. I saw them grow sober, quiet, reverent, respectful, as they realized that this was what God wanted them to hear.

This is God's message, you see. He tells us how hopeless is our condition in order that we might see how hopeful is the condition in Jesus Christ -- and here he has once for all revealed the utter folly of attempting any other approach. He wants us to see the wonderful completeness of the approach that God himself offers us in Jesus Christ. This is why he brings us to this place, because, here in the gospel of the Son of God, we have the perfect answer to all that God tells us we need.

Prayer: Our Father, what folly to try to come in any other way! How foolish we would be -- we poor, mortal men -- to try stand in that august judgment day and know that you are dealing with us on the terms outlined here, when our own heart condemns us, when our own life, our own conscience, writes the word "guilty" against us! Lord, how dare we stand on any other basis than that which is in Jesus Christ -- righteousness made without any works of our own, without any merit of ours, but freely offered to us in him! As we come to Christ just as sinners, needing him, we can be saved. Lord, we thank Thee for this. May this be the day of the beginning of life to many who are yet without Christ. May some speak that word of invitation which says, "Lord Jesus, here is my life, here is my heart, I give it to you. Come and enter and save me, for your name's sake." We pray in his name, Amen."

GOD WILL JUDGE THE SECRETS OF MEN: krinei (3SPAI) o theos ta krupta ton anthropon: (Ro 2:5-note; Ro 3:6-note; Ro 14:10, 11, 12-note; Genesis 18:25; Psalms 9:7,8; 50:6; 96:13; 98:9; Eccl 3:17; 11:9; 12:14; Mt 16:27; 25:31-46; Lk 8:17; Jn 12:48; 1Co 4:5; 2Co 5:10; He 9:27-note; 1Pe 4:5-note; 2Pe 2:9-note; Rev 20:11, 12, 13, 14,15-note)

Secrets (2927) (kruptos from verb krúpto = keep secret, keep safe) refers to that which is hidden, concealed, and kept in secret where no one else can see. 

As a believer I often cringe at the thought of the parallel truth in 1Co 4:5...

Therefore do not go on passing judgment before the time, but wait until the Lord comes who will both bring to light the things hidden in the darkness and disclose the motives of men's hearts; and then each man's praise will come to him from God. (Eg, why am I writing these notes?)

TDNT writes that krupto (krypto)...

has the basic sense “to cover,” “to conceal” (either protectively or for selfish reasons). It then means a. “to bury,” and b. “to set” (of constellations, also used in eclipses). Figuratively it means “to keep secret” (with accusative, double accusative, or preposition, often shameful things), but also “to overlook” and hence “to pardon.”

Kruptos - 17x - Matt 6:4, 6; 10:26; Mark 4:22; Luke 8:17; 12:2; John 7:4, 10; 18:20; Rom 2:16, 29; 1 Cor 4:5; 14:25; 2 Cor 4:2; 1 Pet 3:4. NAS = hidden, 5; inwardly, 1; secret, 7; secrets, 2; things hidden, 2;

Here Paul is referring primarily to the motives that lie behind men’s actions.  The only way to truly judge a person is to judge the secrets of the heart, conscience, and thoughts. Some actions that appear good may be wrongly motivated; other, less visible actions may be done with good intentions. Secret services shall be rewarded, secret sins shall be then punished, and brought to light. To Christians this principle means that God knows everything and that one day we will stand before him to give account of our lives (cf 2Co 5:10).

Alva McAllaster suggested something of this when she wrote a satirical ditty personifying "Envy"...

"Envy went to church this morning. Being legion he sat in every pew. Envy fingered wool and silk fabrics, hung price tags on suits and neckties. Envy paced through the parking lot scrutinizing chrome and paint. Envy marched to the chancel with the choir during the processional. Envy prodded plain Jane wives, and bright wives … and kind men … envy stared."

Do you find her words convicting? If not perhaps you should read them again, this time very slowly. The truth is that envy is not the only "sin" that goes to church. So do sensuality and pride and malice and judgmentalism and many others. And what Paul is saying here is that God knows all of these things.

THROUGH CHRIST JESUS: dia Christou Iesou. (Jn 5:22, 23, 24, 25, 26, 27, 28, 29; Acts 10:42; 17:31; 2Ti 4:1-note; 2Ti 4:8-note)

Through Christ Jesus - Scripture repeatedly attest to the truth that the Son Who is the Savior of all men will one day be the Judge of all men who refuse His gracious offer of salvation while it is still called "Today"...

22 "For not even the Father judges anyone, but He has given all judgment to the Son,
23 in order that all may honor the Son, even as they honor the Father. He who does not honor the Son does not honor the Father who sent Him.
24 "Truly, truly, I say to you, he who hears My word, and believes Him who sent Me, has eternal life, and does not come into judgment, but has passed out of death into life.
25 "Truly, truly, I say to you, an hour is coming and now is, when the dead shall hear the voice of the Son of God; and those who hear shall live.
26 "For just as the Father has life in Himself, even so He gave to the Son also to have life in Himself;
27 and He gave Him authority to execute judgment, because He is the Son of Man.
28 "Do not marvel at this; for an hour is coming, in which all who are in the tombs shall hear His voice,
29 and shall come forth; those who did the good deeds to a resurrection of life, those who committed the evil deeds to a resurrection of judgment. (Jn 5:22, 23, 24, 25, 26, 27, 28, 29) (See also The Two Resurrections - "First" and "Second" - on a timeline)

And He ordered us to preach to the people, and solemnly to testify that this is the One who has been appointed by God as Judge of the living and the dead. (Acts 10:42)

because He has fixed a day in which He will judge the world in righteousness through a Man whom He has appointed, having furnished proof to all men by raising Him from the dead." (Acts 17:31-note)

I solemnly charge you in the presence of God and of Christ Jesus, who is to judge the living and the dead, and by His appearing and His kingdom... 8 in the future there is laid up for me the crown of righteousness, which the Lord, the righteous Judge, will award to me on that day; and not only to me, but also to all who have loved His appearing. (2Ti 4:1,8-See notes 2Ti 4:1; 4:8)

The idea that God will judge the secrets of men by Jesus Christ was distinctively Christian. The Jews taught that God the Father Alone would judge the world, committing judgment to no one - not even the Messiah

Beet notes that Paul