La Genèse 17:1 Halakha : Peninei Halakhah, Family & Mishneh Torah, Circumcision

It is worth noting that the commandment to be fruitful and multiply is mentioned in the Torah well before the commandment of circumcision. It is, of course, more basic and it precedes circumcision. However, it was not said specifically to the Jewish people, but rather shared with all the living creatures on earth, from the fish in the sea to the land animals to man. However, circumcision is the first commandment directed to the Jewish people. Through it, the commandment of being fruitful and multiplying also acquires a deeper meaning. Accordingly, we find that at the time that God commanded Abraham, our father, about circumcision, He promised him the land and the blessing for offspring. As these three basic commandments are all connected, as it is stated: the Lord appeared to Abram and said to him, “I am the Omnipotent God. Walk in My ways and be blameless. I will establish My covenant between Me and you, and I will make you exceedingly numerous.” Abram threw himself on his face; and God spoke to him further, “As for Me, this is My covenant with you: You shall be the father of a multitude of nations. And you shall no longer be called Abram, but your name shall be Abraham, for I make you the father of a multitude of nations. I will make you exceedingly fertile, and make nations of you; and kings shall come forth from you. I will maintain My covenant between Me and you, and your offspring to come, as an everlasting covenant throughout the ages, to be God to you and to your offspring to come. I assign the land you in which you sojourn to you and your offspring to come, all the land of Canaan, as an everlasting holding. I will be their God.” God further said to Abraham, “As for you, you and your offspring to come throughout the ages shall keep My covenant. Such shall be the covenant between Me and you and your offspring to follow, which you shall keep: every male among you shall be circumcised. You shall circumcise the flesh of your foreskin, and that shall be the sign of the covenant between Me and you” (Genesis 17:11).

The foreskin is regarded as an abomination, for which the gentiles are contemned in Scripture, as it is said "For all the nations are uncircumcised (Jer. 9-25). An important institution is Circumcision. For the Patriarch Abraham was not called perfect till he had circumcised himself, as it is said, "Walk thou before me; and be thou perfect. And I will make my covenant between Me and thee" (Gen. 17:1-2). Whoever neglects the covenant of our ancestor Abraham, and retains the foreskin or artificially obliterates the marks of circumcision, even if he has acquired much knowledge of the Torah and practises good deeds, will have no portion in the world to come.