For is a marker of cause or reason between events and carries the idea of because (see terms of conclusion.)

Johnson explains that "for"...

introduces the reader to the reason that there is no condemnation to the one in Christ. And it is the secret of the spontaneous Christian life that lifts one above the bitter exhausting life of the Christian herd (cf. Is 40:31). The gift of the Spirit is the fruit of justification (cf. see Ro 5:5; 7:6 notes Ro 5:5; 7:6), and He operates in the believer's life with the fixedness of a law (the word here probably means something like principle). His leading is not a matter of "sporadic impulse, but the believer's habitual experience" (cf. Gal 5:18; Ro 8:14 see note note). The presence of the sanctifying Spirit, always at work in the life of the believer, confirms the liberation of verse one. Sanctification, I repeat, is a necessary fruit of justification. Thus, a two-fold salvation results from union with Christ, salvation from the penalty of sin and salvation from the power, or bondage, of sin in the daily life. The law of the Spirit of life aids and supports the "law of the mind" (cf, see Ro 7:23- note) on the road to liberty. What we cannot do of ourselves, even when we are the recipients of a new nature, is done for us by the indwelling Spirit. The key to the deliverance of the believer from indwelling sin is the indwelling Spirit of Christ. The measure of His power within us is the life of God, infinite and eternal. In fact, in another place the apostle affirms that the new unit of measurement of the divine power in the believer's life is the resurrection of Christ. The power that raised Him from the dead works is us (cf. Eph 1:20, 21 - see notes; Micah 7:15). The crowning miracle of His life, His resurrection, is seen in His deliverance of us, an amazing fact (Romans 8:1-4) (Bolding added)

Newell offers an interesting comment and challenge noting that...

Here we have at the very beginning of the chapter, one of the most common words of argument in Paul's epistles- for (Greek = gar, Strong's 1063). It occurs some 17 times in this Eighth Chapter, and about one half as many in Chapter Seven, etc. In general, it assigns the reason. Let us not be among those who avoid Paul's epistles because of the mental attention they demand. Most people would rather read a novel or go to the picture shows than study. A chapter with 17 "fors" in it, is closely knit, and must be patiently followed. Unmeasured blessing will result.  (Romans: Verse by Verse)

Paul explains why there is now "no condemnation" for believers. In this next section (Ro 8:2, 3, 4) Paul draws a striking contrast between those who are in Adam and thus can walk only according to the flesh and those who are in Christ and now have a supernatural ability to walk according to the Spirit. We were bound by (enslaved to) sin and death just as we're bound by the law of gravity. It was holding us earthbound or, more accurately, flesh-bound. However, the law of gravity can be overcome by the proper application of certain natural laws, such as the principle of aerodynamics. Though aerodynamics doesn't negate gravity, it can overcome its force.

THE LAW OF THE SPIRIT OF LIFE IN CHRIST JESUS: ho gar nomos tou pneumatos tes zoes en Christo Iesou: (Ro 8:10, 11; Jn 4:10,14; 6:63; 7:38,39; 1Co 15:45; 2Co 3:6; Rev 11:11; 22:1) (Ro 3:21-5:11)

Paul is describing a principle of the spiritual life, like the law of gravity (see below), for one does not have to urge on the "law of gravity" to exert its effect. It does it because that is its natural function. It is like the heart beating. The principle is that it beats without having to be told to do so (excepting of course artificial means of stimulation). In the same way the "law of the Spirit of life" works constantly and will ultimately accomplish His goal of conforming each believer to the image of God's Son (see Ro 8:29, 8:30 see notes Ro 8:29, 30). One is reminded of God's promise to Jacob...

"And behold, I am with you, and will keep you wherever you go, and will bring you back to this land; for I will not leave you until I have done what I have promised you." (Genesis 28:15)

So too the "law of the Spirit" will accomplish what God has promised. There is a new law for the new life. It is here the animating principle by which the Holy Spirit acts as the Imparter of life.

Vine notes that

The phrase “the Spirit of life,” is not subjective, “the Spirit who has life,” but objective, “the Spirit who gives life.” “It is the Spirit who quickeneth” (John 6:63 "It is the Spirit who gives life; the flesh profits nothing; the words that I have spoken to you are spirit and are life."). (Vine, W. Collected writings of W. E. Vine. Nashville: Thomas Nelson)

Law (3551) (nomos) is used in this context to stand for the regulative principle which exercises a control over one. It is analogous to the phrase, the "law" of gravity. Law in this use is not a  reference to the Mosaic law or to other divine commandments or requirements. Nomos is a general "principle" or rule, norm and/or standard of judging or acting. It is the principle by which something else operates (see note) Nomos is used in the sense of a principle of operation earlier in the letter, where he speaks of “a law of faith” (see Ro 3:27 note) and as he does in Galatians, where he speaks of “the law of Christ” (Gal 6:2). The law of the Spirit is higher and more powerful than the law of sin and death.

Stated another way the law is not a written law but a regulative principle which exercises a control over the life of the believer. On the positive side, the regulative control over a believer's life is exercised by the Holy Spirit (although He can be resisted, quenched, grieved, etc which thwarts the efficacy of His supernatural power and work in one's life!). This control is in the form of the "supernatural energy" given the believer both to desire and to do God’s will (see Ezekiel 36:27, Philippians 2:13 - note), this energy coming from the life that God is, which IN the believer is given him by reason of his position in Christ Jesus.

The "principle" of the sin and its association with death is abundantly clear from Romans 7, where we saw the power of sin which brings death as demonstrated by every sin we commit and every cemetery we see. But now in the Risen Christ, Paul instructs us that the "operating principle" of the Spirit of life is stronger than that associated with Sin, and in fact has the inherent power to free us from the operating principle of sin and death, which controls all those who are still "in Adam" and which can still exert its deleterious effects upon those are now "in Christ". But Paul knows that the truth about these two principles has the potential to set his believing readers free to be all they have the potential to be "in Christ."

In short, the power of this new life is the Holy Spirit Who becomes the Almighty Agent within the believer, securing him wholly, making effectual in experience the deliverance which Paul saw when he cried in Romans 7:24-25:

Wretched man that I am! Who will set me free (rhuomai = rescue by drawing or snatching another to oneself and invariably from danger, evil or an enemy) from the body of this death? Thanks be to God through Jesus Christ our Lord! So then, on the one hand I myself with my mind am serving the law of God, but on the other, with my flesh the law of sin.

Of course, the deliverance is through Christ, for it is Christ's Own risen life which every believer now shares ("Christ our life" - Col 3:4-note). But it is the blessed Holy Spirit as "the Spirit of life in Christ Jesus", Who makes the deliverance a reality in our everyday experience. It is the Spirit Who is constantly at work in us to make effectual the deliverance from the "law of sin and of death".

The "law (principle) of the Spirit" is analogous to the "law (principle) of aerodynamics" and it's effect on lifting a plane off the ground thus "countering" effects of the "law (principle) of gravity" (see F B Meyer's note). The Spirit similarly lifts believer's lives to a new plane, to "fly" at a new altitude that heretofore was not possible under the "law of sin and of death" when they tried to attain righteousness in their own power and/or by keeping the Law (or religious rules - anything that we do with the intent to try to make us more pleasing to God. God does not desire our fleshly works or sacrifices but obedience, a broken spirit, a broken heart). We were not justified by faith and we cannot be sanctified by faith (Gal 3:3)...it is a supernatural work of grace of the Holy Spirit of God (Gal 5:1,7). Observe that prior to Romans 8 the Spirit was only mentioned for four times in this letter, but in Romans 8 He is mentioned 19 times making Him clearly a "keyword"!

BEWARE!

The subtle trap one is in danger falling into is in trying to "clean ourselves up" so that we appear more holy. Take for example Paul's story of frustration in Romans 7- it is applicable whether you believe it describes a believer or a non-believer. Romans 7 clearly shows that in the realm of our spiritual life, self (flesh) effort won't work and in fact will leave you in a wretched state! How do we try to "clean ourselves up"? There are many ways we could answer this question. For example, we stop going to R-Rated movies, we stop cursing, etc (and yes, we should stop all of these things) but we think that because we have abandoned a few of the "top five" bad behaviors we are "better" and thus more acceptable to our Father. The Christian life however is not a matter of stopping some things and starting some other things. Paul is saying that now we have experienced a radical transformation and are to order our steps by an entirely new regulating principle, the principle of the Holy Spirit. This distinction may be difficult to grasp, but is worth trying to understand. The question we need to ask ourselves is "Why do I do what I do?" If we can truly say that the Spirit initiated it and energizes it, then glory to God in the highest. If however we initiated it and energized it, no matter how "good" it might appear to others, it is ultimately a work of the flesh. I wrestle with this distinction even as I write these notes...is this flesh or Spirit?

Notice that some of the terminology in this chapter can be confusing. Specifically, true believers although fully capable of behaving quite "fleshly" are strictly speaking no longer "in the flesh" even though the flesh still remains in us. It is a fact that a residual of the flesh nature inherited from our first spiritual father, Adam, still remains in our physical, mortal bodies. But you say "Yes, I know that's true because I still sin. But at least the flesh  is better than it was when I was saved 10 years ago." Wrong! Your flesh and my flesh is no less corrupt, evil, depraved and wicked than it was before our regeneration. "So what's changed?" you ask. Well, what has changed is that flesh now no longer rules in your mortal, physical body like it did when you were "in the flesh". When you were unregenerate in Adam, the flesh was the reigning king. But when you were regenerated, being born from above by the Holy Spirit, the flesh or Old self (old man) was "dethroned" so to speak (the glorious transaction Paul explains in Romans 6:1, 2, 3; 4, 5; 6, 7; 8, 9, 10; 11). But now you have a choice see notes Romans 6:1-3; 6:4-5; 6:6-7; 6:8-10; 6:11). But now you have a choice to make every moment of every day - "Will I obey the flesh or will I obey the Spirit in this particular attitude, action, word or deed?" It's really that simple and yet that profound. We will spend the remainder of our lives learning how to walk in and be controlled by the Holy Spirit, but it is only in this manner that we can experience genuine victory over the old flesh which still lurks within our mortal bodies, seeking to carry out surreptitious attacks that are potentially just as evil and destructive as those it carried out before we were saved. When can the flesh exert control? It occurs when we make a conscious, willful choice to walk in the flesh instead of in the Spirit. Believers have the "mind of Christ" and are called to use their renewed minds to make the choice for God and for His Spirit (realizing that even the "want to" is made possible by a gracious gift of God!). When we make the good, God choice we experience the power not to commit a particular sin as the result of the empowerment and enablement by the Holy Spirit indwelling us and ever leading us to be conformed to the image of God's Son.

"Separation" from the world (sanctification) takes place as we "cooperate" with the Spirit (under control of or continuously being filled with the Spirit...like a "drunk" man...what fills him controls him.) We too, like Paul, have to continually, daily die to the flesh, first saying "yes" to Jesus (arising each morning and choosing to present ourselves to Him as living sacrifices - see Romans 12:1-note) and then much more likely to say "no" to the flesh. Then the Spirit of Christ can live His life through us. It is not us living "like Jesus" trying to do for Him, but Christ actually living His life through us - this is the key to the Christ Life. After all, what happens to the word "Christian" when we take our the name of our Lord? So how can we live this "Christian" life?...

We can't but He can
(Galatians 2:20 -note)

Christ now in us and enables us to do what He has commanded us to do (see Philippians 2:12,13-note). We must come to the wretched end of ourselves (cp Romans 7:24-note), realizing we cannot live the life Christ lived unless He lives it through us, in the power of His Spirit, and ultimately for the glory of His Father. Have you reached this "wretched point" in your life? Take heart, there is great hope in Romans 8 for

"the path of the righteous is like the light of dawn, that shines brighter and brighter until the full day." (Proverbs 4:18)

Larry Richards has an insightful comment on the victory available to every believer in Romans 8 explaining that...

Sin within is overcome by a new and powerful principle, that of “the Spirit of life.” Put simply, Paul found his answer in realizing that even as a believer he could not keep the Law … and was no longer trying! Paul no longer felt any obligation to try! Paul had finally accepted himself as really a sinner, with no hope of pleasing God. So Paul turned his gaze back to the Cross, and found joy in the thought of “no condemnation.” But then Paul made the great discovery! When he stopped trying, and instead relied on God to express His own divine life through Paul’s personality, then “the righteous requirements of the Law” were “fully met” in him (Ro 8:4-note). Sin lived in Paul. But Christ lived in Paul too. If Paul concentrated on keeping the Law rather than on trusting Jesus, his old nature was stimulated and he sinned. When Paul concentrated on trusting Jesus, the Spirit energized his new nature and he found himself living a righteous life. Our obligation, then, is not to the Law, but to respond to the leading of the Holy Spirit (Ro 8:12-note, Ro 8:14-note). The Law has been replaced by an intimate, personal relationship with God.

Baseball provides an analogy. We want to get to first base. But to do so the batter does not look at first base. He watches the ball. He focuses all his energy in concentrating on hitting the ball as it is pitched. In a sense the “righteous requirements” of the Law are first base to us. We yearn to get there. But too many believers focus their attention on first base—and constantly strike out! What Paul said was keep your eye on the ball—on Jesus Himself—and you will discover that you arrive on first base (a righteous life) without even trying. (Ed note: Not exactly in my opinion - e.g., see Philippians 2:13- note)

How can relationship be the key to moral victory? How does relationship produce righteousness? Paul showed us that as we deepen our relationship with the Lord, the Spirit of God gains more and more control over our lives. Then the Spirit will “give life to your mortal bodies” (Ro 8:11-note). Yes, in our mortality we are in the grip of sin. It has always taken resurrection, life from the dead, for God to express Himself in human beings. And resurrection is exactly what God provides for those who “live in accordance with the Spirit” and “have their minds set on what the Spirit desires” (Ro 8:15-note). (Richards, L., & Richards, L. O.  The Teacher's Commentary. Wheaton, Ill.: Victor Books)

Notice the precious and magnificent promises that the Holy Spirit provides for every believer in Romans 8:

Freedom (Ro 8:2-note)
Strength for service (Ro 8:11-note)
Victory over sin (Ro 8:13-note)
Guidance (Ro 8:14-note)
Witness of sonship (Ro 8:16-note)
Assistance in prayer (Ro 8:26-note)

Henry Morris explains that...
 

"The "law of the Spirit of life" has invaded and opposed "the law of sin which is in my members" (Romans 7:23-note), thus freeing us from its bondage (Romans 6:12, 13, 14, 15, 16, 17 see notes on Romans 6:12-14 6:15-17). We cannot obey God's law in the strength of the flesh, but as we reckon (that is, deliberately acknowledge) ourselves to be dead to sin and "alive unto God" (see Romans 6:11-note) this doctrinal truth increasingly becomes practical truth in our lives." (Defender's Study Bible)

Newell writes that...

John Wesley's testimony is well known, concerning the beginning of his life of real faith (in his 35th year, after 13 years in a relatively commonplace ministry):

"In the evening I went very unwillingly to a society in Aldersgate Street where one was reading Luther's preface to the Epistle to the Romans. About a quarter before nine, while he was describing the change which God works in the heart through faith in Christ, I felt my heart strangely warmed. I felt I did trust in Christ, Christ alone, for salvation; and an assurance was given me, that He had taken away my sins, even mine, and saved me from the law of sin and death.

For the next 53 years Wesley was "the outstanding figure and the greatest force in the English speaking world." But notice that he realized at Aldersgate Street, the two great elements of our salvation:

(1) forgiveness of sin's guilt; and
 

(2) deliverance from sin's power - from the law of sin and death.'
 

(Romans: Verse by Verse)

Alford says that...
 

“This law of the Spirit of life having freed him from the law of sin and death, so that he serves another master, all claim of sin on him is at an end—he is acquitted, and there is no condemnation for him.”

HAS SET YOU FREE: eleutherosen (3SAAI) se: (Ro 6:18,22; Ps 51:12; Jn 8:32; 2Co 3:17  Gal 2:19; 5:1)

Has set you free (1659) (eleutheroo = the ending " -oo" means not only will it be set free but it will be seen as set free)  means to cause someone to be freed from domination. The picture is that of the emancipation of slaves. The idea is that the one set free is at liberty, capable of movement, exempt from obligation or liability, and unfettered. Although the act of setting free results in freedom and liberty we must understand that this new freedom is not a license to sin. In fact true liberty for the believer is now living as we should and not as we please. 

Eleutheroo is used 7 times in the NT -- Jn 8:32, 36; Ro 6:18-note, Ro 6:22-note; Ro 8:2-note, Ro 8:21-note; Gal. 5:1  (and only in Pr 25:10 in the Septuagint