Romans is a theological argument for the gospel in the form of a letter to the church in Rome. The church had both Jewish and Gentile members. Throughout the book, Paul will argue for the unity of Jews and Gentiles, both in God's condemnation of their sin, and of salvation for both through the gospel. In chapter 1, Paul revealed the sin of the Gentiles and God's condemnation of it. In chapter 2, Paul exposed the sin of the Jews. They thought their membership in old covenant family, shown by their circumcision, would save them no matter what. Paul said no, Jews are indeed under condemnation for sin unless they have obeyed the law perfectly. And they had not.
Paul shows that the true people of God (the church) are not that because of outward signs, such as physical circumcision. Rather, they belong to God because he changed their heart, symbolized by the term "circumcision of the heart". (29) It is a change caused by the Holy Spirit, not by the law. It is demonstrated by a desire to please God and not man.