And it's just as useless for attaining salvation as the old circumcision.
Romans 2:25-29 25For circumcision indeed is of value if you obey the law, but if you break the law, your circumcision becomes uncircumcision. 26So, if a man who is uncircumcised keeps the precepts of the law, will not his uncircumcision be regarded as circumcision? 27Then he who is physically uncircumcised but keeps the law will condemn you who have the written code and circumcision but break the law. 28For no one is a Jew who is merely one outwardly, nor is circumcision outward and physical. 29But a Jew is one inwardly, and circumcision is a matter of the heart, by the Spirit, not by the letter. His praise is not from man but from God.
Romans 4:1-12 1What then shall we say was gained by Abraham, our forefather according to the flesh? 2For if Abraham was justified by works, he has something to boast about, but not before God. 3For what does the Scripture say? "Abraham believed God, and it was counted to him as righteousness." 4Now to the one who works, his wages are not counted as a gift but as his due. 5And to the one who does not work but believes in him who justifies the ungodly, his faith is counted as righteousness, 6just as David also speaks of the blessing of the one to whom God counts righteousness apart from works: 7 "Blessed are those whose lawless deeds are forgiven, and whose sins are covered; 8blessed is the man against whom the Lord will not count his sin."
9Is this blessing then only for the circumcised, or also for the uncircumcised? We say that faith was counted to Abraham as righteousness. 10How then was it counted to him? Was it before or after he had been circumcised? It was not after, but before he was circumcised. 11 He received the sign of circumcision as a seal of the righteousness that he had by faith while he was still uncircumcised. The purpose was to make him the father of all who believe without being circumcised, so that righteousness would be counted to them as well, 12and to make him the father of the circumcised who are not merely circumcised but who also walk in the footsteps of the faith that our father Abraham had before he was circumcised.
Galatians 5:1-6 1For freedom Christ has set us free; stand firm therefore, and do not submit again to a yoke of slavery. 2Look: I, Paul, say to you that if you accept circumcision, Christ will be of no advantage to you. 3I testify again to every man who accepts circumcision that he is obligated to keep the whole law. 4You are severed from Christ, you who would be justified by the law; you have fallen away from grace. 5For through the Spirit, by faith, we ourselves eagerly wait for the hope of righteousness. 6For in Christ Jesus neither circumcision nor uncircumcision counts for anything, but only faith working through love.