Romans 2:26-29 :
If therefore the uncircumcised keep the ordinances of the law, won’t his uncircumcision be accounted as circumcision? Won’t the uncircumcision which is by nature, if it fulfills the law, judge you, who with the letter and circumcision are a transgressor of the law? For he is not a Jew who is one outwardly, neither is that circumcision which is outward in the flesh; but he is a Jew who is one inwardly, and circumcision is that of the heart, in the spirit not in the letter; whose praise is not from men, but from God.
Circumcision was the way that the Jews identified themselves with the Law of God. It was an outward act that showed that they were following The Law of God. As we all know, outward acts often end up being only that and have no reality in the mind or heart of a person.
Some of the Jews had made their religion an outward thing only. Paul explains that this is not God’s intent. God expects a Jew to be a Jew inside the heart. That is why Jesus came. He was able to change the heart of those who were not even outwardly Jewish. You will remember this fact if you went through our study in Acts. Many Gentiles came to know Jesus and never became Jews first. In reality, those who do what God wants from their hearts are really acting more like Jews than Jews who say they are Jews but disobey in their hearts.
As Christians, we are identified with God because our spirits have been changed. Because God did this for us, we are able to live as God wants.
It is good to recognize here that the Jewish religion was an outward one that exposed an inward problem. Going back to following an outward religion that exposes problems is not appropriate for us today since we now have a solution to our problem of sin through Jesus. Once sin is taken care of, we are actually able to live righteously from the heart.