It is clear from Paul’s description here that the Jews in the main assumed that mere possession of the written law and the ritual of circumcision was sufficient to give them a standing before God and before other humans as well. How did the Jews relate to the law?
They relied upon it and used it as the way to get to know God and his will. Further, they communicated it to others as the best way to live. Initially we might respond and say that this was a good way to proceed with using the law.
But they did not seem to realise that a failure to keep it perfectly invalidated their claims as to what it could do. Instead of leading people to praise God, the failure of the Jews confirmed the Gentiles in their own behaviour and caused them not to want to have anything to do with God and his law. So instead of being influential for God, the Jews were the opposite. Of course, Paul is speaking here as an eyewitness. He had seen numerous failures of the Jews to keep God’s law and provides several examples of where they failed.
What is striking is not their failures, but their response to them. Instead of repenting, they persevered in attempting to live by the law and to get others to live by it as well. And the way in which they revealed this response was to stress the importance of circumcision.
The Jews believed that circumcision provided them with security and marked them out as authentic in God’s sight. After all, did God not give this sign to Abraham in order to distinguish them as a people from all others? Yet it was also the case that those who had been circumcised had to keep the law. If they failed to keep it, they would just be the same as the uncircumcised as far as God was concerned. Both groups were disobeying his law.
Paul even mentions the hypothetical example of a Gentile perfectly keeping the law written on his heart. Would such an uncircumcised person not be as true to God as a circumcised person who kept the law? That uncircumcised person could easily condemn any circumcised person who failed to keep the law totally. The point is what a person is within, in his heart, and not what religious rites he engages in.
In contrast to the Jew described in verses 17-24, a real Jew, says Paul, is the person who has experienced inner renewal, described here as circumcision of the heart, which is another way of saying that such a person has a new heart created within him by the Holy Spirit. With that inner renewal, there will be outward obedience and the individual will then please God. Paul here is dropping hints about the Christian life that he will develop later in Romans. But the point at present being stressed is that mere possession of the law or participation in a religious rite such as circumcision does not prove anything.