In Romans 4:1-15, Paul has argued that Abraham was justified by faith apart from works of the law and apart from circumcision. Then comes 4:15a, "because the law brings about wrath;" But then he says in 15b, "And where there is no law there is no transgression."
Why was this 15b written? What is the point after what was said before? I don't see how "transgression" enters the flow of text.
The argument is built in order to show us why the basis of the promise must be by faith rather than of works.
First we must distinguish between sin and transgression.
Sin is missing the mark and falling short of the perfect will of God.
Transgression, however, is a violation of a known law. It is a willful crossing of a boundary. You can’t transgress a boundary that hasn’t been drawn. The law drew that boundary. For example, one might trespass on someone's property by accident. Alternatively, if someone sees a “No Trespassing” sign and crosses the boundary anyway, then it’s a violation of a known law and therefore a tresspass. The law was needed for volition and for sin to be imputed:
for until the Law sin was in the world, but sin is not imputed when there is no law. (Romans 5:13)
Let's look at the full case made:
13 For the promise to Abraham or to his descendants that he would be heir of the world was not through the Law, but through the righteousness of faith. 14 For if those who are of the Law are heirs, faith is made void and the promise is nullified; 15 for the Law brings about wrath, but where there is no law, there also is no violation. (Romans 4:13-15)
If the promise was based on the law, it would only result in wrath, because the law is what gives transgressions their definition and thus exposes and multiplies them. The law therefore brings wrath because it turns sin into transgression, which is a legal violation.
In other words, the reason for using "transgression" was to make the point that faith, not law, must be the basis of the promise because the law made sin explicit, accountable, and therefore more condemnable.
The opening verses of chapter 4 provide the hermeneutic context for what is stated in verse 15.
Paul cites Abraham as believing the promises of God (even though he had to wait decades for the promise of a God-provided heir, then showed faith in being prepared to later sacrifice that heir, at God's command). God had not yet given his perfect Law for his people, at Sinai. Yet Abraham walked with God, in faith, believing God.
Lawlessness can be either ignoring law - living without regard to law - as well as deliberately breaking law. When it is the law of God that people either think they can do without, or view their failures as being just brushed aside by God, they sin. And, "The wages of sin is death" (Romans 6:23). Sinners are never viewed by God as being righteous: "For there is no-one righteous, no, not even one" (Romans 3:10); and
"...the righteousness of God [is] through the faith of Jesus Christ to all, and upon all those believing - for there is no difference, for all did sin, and are come short of the glory of God - being declared righteous freely by His grace through the redemption that [is] in Christ Jesus." Romans 3:22-24 YLT
The righteous Law of God is perfect because God is perfect. This means that as nobody is righteous, nobody can perfectly keep God's perfect law and will thus be judged a sinner by God. That is why the scripture states that
"For whosoever shall keep the whole law, and yet offend in one point, he is guilty of all." James 2:10 A.V.
This offends people who fail to realise that this speaks of God's perfect law; not human law. Knowing that no sinner could ever keep his law, God provided the way in which repentant sinners could have all their sin dealt with by him, in righteousness. To those who put faith in that provision of grace - Christ bearing the wrath of God for sin, though he was sinless - this applies to those who were dead in their sins but whom God raised to new life, in Christ:
"[God] made alive together with him, having forgiven you all the trespasses, having blotted out the handwriting in the ordinances that is against us, that was contrary to us, and he hath taken it out of the way, having nailed it to the cross." Colossians 2:14 YLT
The perfect law that condemns us, has been taken out of the way, being symbolically nailed to the cross. It takes faith to believe what Christ accomplished, but once the magnitude of what was righteously achieved is believed by us in faith, we are forgiven; not because we did anything to deserve forgiveness - quite to the contrary - but because this is the gift of God to all who put faith in the Son. Then we can walk with God, in faith, believing God, as did Abraham.
To such ones, the law that was against them has been taken out of the way, by God. Our transgressions have thus been lifted up and away, through his righteous transaction at the cross. That is why Paul could say in Romans 4:15 that now there is no law, and thus no transgression - for those of faith.
