For circumcision is indeed profitable if you keep the law; but if you are a breaker of the law, your circumcision has become uncircumcision. 26 Therefore, if an uncircumcised man keeps the righteous requirements of the law, will not his uncircumcision be counted as circumcision? 27 And will not the physically uncircumcised, if he fulfills the law, judge you who, even with your written code and circumcision, are a transgressor of the law? 28 For he is not a Jew who is one outwardly, nor is circumcision that which is outward in the flesh; 29 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. — Romans 2:25-29.
A true Jew is one ‘who is one inwardly’. Those who rely on outward circumcision, yet still live sinful lives of unbelief and rebellion, are not really Jews at all! The inward circumcision that counts is not like the putting away of the flesh outwardly, but is the cutting of sin from the human heart by God’s Spirit in the new birth produced by the gospel (cf. Colossians 2:11 onwards). It is spiritual and can be known by Jew or Gentile who trusts in Christ. [Sourced from The Bible Panorama.]