Galatians 3:8 And the Scripture, foreseeing that God would justify the Gentiles by faith, preached the gospel to Abraham beforehand, saying, “In you all the nations shall be blessed.
Abraham was circumcised at the age of 99 years old - a covenant between him and God.
Genesis 17:1 When Abram was ninety-nine years old, the LORD appeared to Abram and said to him, “I am Almighty God; walk before Me and be blameless.
Genesis 17:10-11 This is My covenant which you shall keep, between Me and you and your descendants after you: Every male child among you shall be circumcised; and you shall be circumcised in the flesh of your foreskins, and it shall be a sign of the covenant between Me and you.
For he who is keeping the law, it is circumcision and will become uncircumcision when he breaks the law.
Romans 2:25 For circumcision is indeed profitable if you keep the law; but if you are a breaker of the law, your circumcision has become uncircumcision.
It's not the cut of a knife that makes a Jew. You become a Jew by who you are.
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 from men but from God.
Abraham is a Gentile and was circumcised of the flesh, and so are we.
2 Corinthians 3:6 who also made us sufficient as ministers of the new covenant, not of the letter but of the Spirit; for the letter kills, but the Spirit gives life.