Romans 4:13-15 meaning

In the process of furthering his argument that faith is the path to righteousness rather than law, Paul clarifies something here: Abraham's descendants are those that come to righteousness through faith, not the law: 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 (v 13).

Believing in Jesus allows us to receive the righteousness of God in the eyes of God, based on the work and decision of God and God alone (Romans 4:1-3). We belong to God and God's family unconditionally from the minute we first believe in Christ. Thus, as Paul will continue to explain, those of us who believe in the gospel of Jesus are heirs with Abraham (v 24) because Abraham's faith was what God credited to him as righteousness (v 3).

If it was through the law that we were made heirs with Abraham—if we had to be circumcised, etc.—that wouldn't make sense because Abraham's faith is what counted, not his works. Paul argues that if keeping the law is necessary to be righteous and to inherit the blessings of the promises of God, then the promise to Abraham would no longer be in effect: For if those who are of the Law are heirs, faith is made void and the promise is nullified (v 14). And that would mean God had overturned His promise by bringing in the law. God always keeps His promises, so this is not possible.

This is turning the tables against the line of argument brought by Paul's adversaries, the competing Jewish "authorities." These "authorities" have claimed that Paul is setting aside the law with his gospel. Paul has called their claim "slander" (Romans 3:8). Paul's ministry partners Aquila and Priscilla host a church in their house in Rome, and are doubtless combatting the same slander from these adversaries (Romans 16:3, Acts 18:2, 18, 26). Now Paul shows, conversely, that his adversaries' argument is one that sets aside the promise of God in favor of the law.

Jesus came to bring righteousness apart from the law (Romans 3:21). This was a continuance of the promise Abraham believed, apart from the law, resulting in God declaring Abraham righteous (Romans 4:3). Paul is continuing the thought here that adding the law as a requirement for righteousness after God declared Abraham righteous by faith would necessarily add wrath to Abraham and nullify the promise God made: For the Law brings about wrath, but where there is no law, there also is no violation (v 15).

Since God makes us righteous apart from the law, the fact that we break God's law does not bring the wrath of the Law, which is the punishment of being separated from God's eternal family. Rather, God's grace spans the gap between us and God. Since the law has been removed for us, there is no violation of the Law, and therefore we avoid forever the wrath that is the eternal penalty of sin. Every sin was nailed to the cross with Jesus (Colossians 2:14). Therefore, when we receive the free gift of Jesus by faith, we receive the benefit of Jesus having born the wrath of our sin (John 3:14-15).