Romans 2:29

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 of men, but of God. [He is not a Jew in God's sight (though he is, of course, such in the sight of the world) who is simply one without; i. e., by being properly born of Jewish parents, nor is that a circumcision in God's sight (though it is in the sight of the world) which is merely fleshly. But he is the real, divinely accepted Jew who is one within; i. e., who has in him the spirit of Abraham and the fathers in whom God delighted (John 1:47). His life may be hid from men, so that they may see nothing in him to praise, but it is praiseworthy in the sight of God, and circumcision is not that outward compliance with the letter of the law--literal circumcision--but that inward spiritual compliance with the true meaning of circumcision, the cutting off of all things that are impure and unholy, and that make the heart unworthy of an acceptance into the household of God.]