Romans 2:25-28

If you follow the law, your circumcision has meaning. But if you break the law, it is as if you were never circumcised. People who are not Jews are not circumcised, but if they do what the law says, it is as if they were circumcised. You Jews have the written law and circumcision, but you break the law. So those who are not circumcised in their bodies, but still obey the law, will show that you are guilty. They can do this because a person is not a true Jew if he is only a Jew in his physical body; true circumcision is not only on the outside of the body.