In Romans 2, Paul says that the Jews were guilty of blaspheming the name of God by trying to enforce the Law on the Gentiles.
Paul said God judges the heart. All who sin without the Law will perish without the law, and all who sin under the Law will be judged by the law. Men are not righteous simply because one hears the rules presented in the law. Those who uphold the values and morals given in the Law are the ones justified.
Paul said Gentiles do not have the Law. Yet, by nature, they do what the Law requires. In doing so, they are a "law" to themselves. Our "law" is written on our hearts, and Paul said that our conscience is our guide. Though we have conflicting thoughts of accusation or even thoughts that excuse us from portions of the Law, Paul said that our conscience is the one that bears witness for us. God judges the secrets of the hearts of men by Christ Jesus, not the rules we impose.
Paul said the Jews were hypocritical, and were blaspheming the Name of God in their attempt to impose the rules of the Law to the Gentiles. He said that it was prophesied in scripture that they would do so.
The Jews were given law that was excellent, because they were to be a guide to the blind Gentiles living in darkness. They were presented with the knowledge and Truth. Yet, as men, they were not perfect. They preached against stealing, yet they themselves broke the commandments in either their hearts or their actions. Adultery, idolatry, and more, they were guilty of breaking the Law they tried to enforce upon the Gentiles.
Paul said that those who boast in the law dishonor God. They were guilty of breaking the Law, and this was blasphemy.
Paul said that if we rely on following the rules by the letter, or exact words in which they were written, our praise is from man and not from God. Our circumcision is one that comes from the heart, not from the physical actions. If our interpretation of righteousness is simply by obeying rules, then our "circumcision" becomes "uncircumcision." Yet, if we who are "uncircumcised" keep the precepts of the law -- the foundation for our moral conduct -- we become "circumcised" by our hearts.
They were Jews, and they were trying to teach the rules of the Law to the Gentiles. The Law was given to the Jews. Paul said that Jews are not Jews by their outward attempt at keeping Law, they were Jews inwardly from their heritage. He said the same about "circumcision." It is not an outward and physical display of following rules, circumcision is a matter of the heart and by the Holy Spirit. Our praise is from God.
As Christians, we should ask ourselves: Have we blasphemed the Name of God by condemning others in their walk with Christ? Are we guilty of laying down rules of the Law that we break daily? Have we looked down on others who are circumcised by the Holy Spirit?