“25 For circumcision indeed is of value if you obey the law, but if you break the law, your circumcision becomes uncircumcision. 26 So, if a man who is uncircumcised keeps the precepts of the law, will not his uncircumcision be regarded  as circumcision? 27 Then he who is physically uncircumcised but keeps the law will condemn you who have the written code  and circumcision but break the law. 28 For no one is a Jew who is merely one outwardly, nor is circumcision outward and physical. 29 But a Jew is one inwardly, and circumcision is a matter of the heart, by the Spirit, not by the letter. His praise is not from man but from God.” (Romans 2:24-29 (ESV)
But a Jews is one inwardly, and circumcision is a matter of the heart, by the Spirit, not by the letter.
The Old Testament is replete with references to a circumcision of the heart. The idea was that the people though they had been circumcised in the flesh of their foreskins were not lovers of the law. They did not love God with all their heart, will all their mind and with all their strength, they did not love their neighbors as themselves. The people did what they wanted when they wanted. At other times, they followed the law out of love for themselves but without any care for their neighbors, it led to a lack luster performance of priests passing by on one side, Pharisees on the other, veering off the way of the Lord, parting from God’s law to the left or to the right when the proper thing, the loving thing was to pick up the man bludgeoned and left for dead in the middle of the road and take him to an inn. God desires mercy and not sacrifice. Love is what fulfills the law. What is spoken of here as a circumcision of the heart is a heart that loves, because a heart that loves loves the law of God that shows it what it means to love. This is the work of the Spirit. Not the law, not the letter but the Spirit, who calls us by the gospel, which is the love of God poured out for us in the blood of his Son Jesus Christ, who first loved us that we might love.