Just as with the 2nd chapter, Romans suffers from horrible editing. So we need to spool back to verse 21 of the previous chapter, (which is the natural starting point for a new chapter), and proceed from there.
At the end of the previous chapter, Paul established that righteousness now comes through faith in Christ, not through Law-keeping. This is of course a radical proposition. Under the Old Covenant, the standard of right and wrong was the Law, and therefore wrong-doing and right-doing, sinfulness and righteousness, were adjudicated and perceived in terms of how well or badly you kept to the Law. If you stole something you were unrighteous, if you obeyed the Law in all aspects, like the rich young ruler, (Mark 10:17-27), you were considered righteous. Now Paul is explaining the New Covenant to us. Righteousness comes from faith in Christ, and is freely available to all mankind. When Jesus offered himself up as a sacrifice, he atoned for all mankind’s sins. We have gone from a law-abiding Kingdom to a faith-abiding Kingdom.
Paul now puts Jesus’s sacrifice into the bigger picture of the Abrahamic faith covenant, in which Abraham is considered as the father of faith. Abraham believed God at every turn. He believed God when he was told to uproot to a foreign country, and he believed God’s promises to him, that even though he and Sarah were centurions or thereabouts, that they would have a child, who would be the forefather of many nations. Paul tells us that God accounted Abraham’s belief as righteousness. He then explains that Abraham believed God prior to the institution of Israel; the stamp of authentic membership of Israel was circumcision, and Abraham received this after he had entered into the faith covenant with God, the stamp was merely the mark of approval. (Abraham received the promises and went to Canaan when he was 75, some 15 years before the Abrahamic Covenant and the creation of Israel.)*. So Paul establishes the faith covenant as pre-existing Israel, and therefore he needs no further validation for the covenant extending beyond Israel and to all mankind. He then further clarifies that ‘the heirs to the world’ (Gen12:2-3) are the ‘faith people’, (i.e. the Church), and not ‘the Law people’, i.e. physical Israelites, as the promise of the world, i.e. of a great nation who would bless the entire world, was granted to Abraham on the basis of his faith. Paul wryly observes that if the promise goes to the Law people, then the promise becomes null and void, because the Law ends in wrath, i.e. there would be nobody to inherit it.