There are 5 warnings in Hebrews.
Hebrews 3:6+ "IF" is 3rd class conditional which conveys the idea of doubt in regard to what follows. The writer is saying "You know the truth but you've not responded to it". There is a difference in hearing & obeying. As John says if they really were of us (true believers) they would not have left us (1Jn 2:19+). In Hebrews 3:7+ the "says" is present tense meaning that the Holy Spirit continues to illuminate truth to us. "Today" in Heb 3:7 is not as distinguishable or distinct as different word for "day" in Heb 3:8. The "if" in Hebrews 3:6+ is also a 3rd class conditional "if" expressing some doubt. "Hear" in Hebrews 3:7+ means to hear with the intention of doing something about what you hear. Voice means that which explains what one has in mind for others. God has explained it in His Son & His Spirit continues to bring that message to us.
CHARACTERISTICS OF UNBELIEF
(NON-BELIEVER)
1). Stubborn:
Hebrews 3:8+ "Harden" (skleruno in aorist subjunctive) means to become rigid or stiff, to refuse to change, used 4x in Hebrews (Heb. 3:8; Heb. 3:13; Heb. 3:15; Heb. 4:7). The use of "heart" (kardia) in Scripture is closely linked to soul and mind and deals with the thoughts, understanding, reasoning and will. All of these are involved when a person is saved. A person may understand the truth but refuse to submit his will and come to a point of commitment. Don't be like your forefathers who refused me for 40 years. You don't get what God's promised you until you are willing to do what God said to do. Unbelief is stubbornness. It is not that they don't know what to do but that they refuse to submit their will.
2). Shamefulness: blinded to the offense that unbelief is against a holy God.
Provoked (parapikrasmos) = cause to anger. In day of temptation = the 40 year period of wilderness wandering. Why did they provoke God? They were unwilling to do what God told them to do. This offends a holy God. Tried (peirazo) Me = to prove something as evil. Testing (dokimazo) = to test to prove something good. When you refuse to believe what you know as truth, then by your own unwillingness to obey, you make God appear to be evil, as if He is not worthy to be obeyed. But even when they tried God, ultimately they found out that He was good because they saw His works for 40 years. Isn't it amazing when people deny what they know to be true even though they have seen His works that show His goodness! If I am not willing to obey the very same words I tell my children to obey, then I am proving by my example that God is not worthy to be in control of my life. In Hebrews 3:10+ "angry" (prosochthizo) is grieved, disgusted, loathed. In Heb 3:11+ note when God swears that settles the issue! Wrath = desire with grief, i.e., He desired to make them hold fast to a standard that He had held up but He was grieved that He had to do it. Acts 7:49+ 'HEAVEN IS MY THRONE, AND EARTH IS THE FOOTSTOOL OF MY FEET; WHAT KIND OF HOUSE WILL YOU BUILD FOR ME?' says the Lord; 'OR WHAT PLACE IS THERE FOR MY REPOSE?' One of the meanings of "rest" is abode or dwelling place referring in Hebrews 3:11+ to Canaan. This word for "rest" (katapausis) is only used in Acts 7:49+ & in Hebrews (Acts 7:49; Heb. 3:11; Heb. 3:18; Heb. 4:1; Heb. 4:3; Heb. 4:5; Heb. 4:10; Heb. 4:11) They forfeited God's rest which is what disbelief does.
3). Senseless: don't go back under the Law.
Hebrews 3:10+: Always go astray (planao) = passive voice meaning they did not voluntarily do it but were made to go astray. Why? Because they had refused to obey what God had said, which caused them to lose direction in their life. Unbelief is stupid. They came out (Egypt) to go in (Canaan) (Dt 6:23+) but by their own stubbornness they forfeited the very thing they wanted, the very thing God wanted to give them. Proverbs 5:22+ says a man is bound by the cords of his sin. An unbeliever is fooling himself, thinking he's getting what he wants but he forfeits what he needs. The flesh always kicks against the very things I need in my life. Senseless! Nobody wants to go to the Cross, the very thing we need.
THE CASUALTY OF UNBELIEF:
APOSTASY
1). Deceit of an Apostate: He may be in church, singing the same hymns, etc. but is still not a true believer.
He shames the living God because he will not bow before the truth. He is knowledgeable. "Take care" (present imperative see our need to depend on the Holy Spirit to obey) in Hebrews 3:12+ is "watch out!". Evil = not kakos which is inherent evil, e.g., we may be doing "good" things in our flesh, asking God to bless them but they are "evil" because they were initiated by our flesh not by Him. Remember Aaron's 2 sons struck dead because they brought "strange fire" before God (Nu 26:61+). Many will perform "religious" activities to keep from having to bow before the Cross. But when I come to Him as Lord and Savior bowing before Him, He then becomes the Initiator in my life and that's where true righteousness comes from. The word for "evil" used here is poneros, a malicious, active, aggressive type of evil. The apostate's heart is full of unbelief, totally devoid of the ability to trust God and he totally refuses to submit to what he knows to be true.
No root. No fruit.
The apostate has chosen to reject Christ: He may embrace the church & Christians but he has never embraced Christ. "Falling away" (aphistemi giving us English "apostate") is aorist tense speaking of a point in time when he made a choice to not have anything to do with the claims of Christ. Apostate (apo = away from) is one who has chosen to stand away from. Luke 8:6, 13+: Parable of the Soils: Describes the rocky soil, which receives Word with joy, but has no root, so they believe for a while, and in time of temptation fall away (aphistemi). No root. No fruit. Why does he fall away? "Temptation", persecution just like the Hebrew believers were experiencing! When a person continues to harden his heart, he will eventually get to the point where he makes the choice to walk away from the living God.
2). Defense Against Apostasy: Keep on exhorting one another daily.
The writer knows there are those in the midst of the congregation who have not yet submitted to Christ as Lord. In Heb 3:13+ "hardened"(skleruno) is aorist passive voice meaning the hardening is being produced in us by an outside force. Hardening here gives us English atherosclerosis which doesn't happen overnight, but slowly over time. Therefore the exhortation to encourage one another DAILY while it is still today. How? By raising the standard of living a holy life, of dependence upon God, of walking in faith. If we don't do that daily, someone amongst us who is continuing to be hardened will soon apostatize. Therefore encourage (parakaleo) one another daily (Hebrews 3:13+). Deceitfulness (apate) means the deceitful influences of sin. Sin here is the attitude of sin, the root of which is failure to depend upon God. We must encourage each other daily to depend upon God. If one is lured into the lie that he can get along without God, that you don't have to really trust Him, over a period of time that person will be hardened (passive voice) and eventually will defect from the faith (apostatize). If you are living without faith, those around you can see and the result can be a hardening of those watching your life.
3). Demise of the Apostate: Failure to enter into His rest.
1,600,000 Israelites (except for Joshua & Caleb) failed to enter into Canaan. 1 Co 10:1-11+ says a similar thing describing many with whom God was displeased. Remember when there is no root, there is no fruit and the "fruit" he mentions in Hebrews 3 is continuance in the faith. You may fall into a sin but you cannot live continuously in a state of lawlessness according to 1 Jn 3:10+. So when these apostates experienced a little pressure and persecution, they checked out, returning to the Law. But what does the Law force one to do? Work (Ro 7:5+). What happens when you cease to work? Rest! And they failed to enter His rest. Jesus said "Come unto Me all ye that labor and are heavy laden and I will give you rest." (Mt 11:28+)
Is it a "passive rest"? No way. He will wear you out! But this rest is resting from fleshly "works". Those who do not enter, but work to please God, force their legalistic standards on those around them. They say that if you don't live up to their standards, you will not be pleasing to God. A legalist tries his best to do "one more work for God" and it is never enough but there is no condemnation for those who are in Christ Jesus (Ro 8:1+). We don't do what we do to please God. We do what we do because we are ALREADY pleasing to God. There's now a different motivation for the whole Christian life. Enter into the rest of grace. We can now do nothing to cause us to not be accepted in the Beloved (Eph 1:6KJV+). He unconditionally loves us. How sad that many kick against the goad of the Cross (Acts 26:14+), the very thing they need to set them free from their works mindset. They want religion but apart from the death to self. "Praise" in Hebrew also means confession of sin. Praise in your walk affects praise in your worship. We praise Him in our walk when we have died to self, reckoning ourselves dead because we already are (Ro 6:11+). The victory was sealed at the Cross and we are complete in Jesus (Col 2:10+). The kindness of God is what brings a man to repentance (Ro 2:4+).