Берешит 17:2 Галаха: Mishneh Torah, Circumcision

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.

Mark how strictly the observance of Circumcision is to be regarded. Moses, although he was on a journey did not receive indulgence a single hour for neglecting this duty. In connection with all the precepts of the Torah, three covenants were made with Israel; as it is said "These are the words of the covenant which the Lord commanded … beside the covenant which He made with them in Horeb" (Deut. 28:69). And in the next section it is said "Ye are standing this day all of you before the Lord your God … that thou shouldst enter into the covenant of the Lord thy God" (Deut. 29:9-11). Three covenants are here mentioned. But in connection with Circumcision, thirteen covenants were made with our ancestor Abraham: "And I will make My covenant between Me and thee" (Gen. 17:2); "As for me. behold, My covenant is with thee" (ib. 17:4); "And I will establish My covenant between Me and thee" (ib. 17:7); "for an everlasting covenant" (ib. 17:7); "And as for thee, thou shalt keep My covenant" (ib. 17:9); "This is My covenant which you shall keep" (ib. 17:10) "And it shall be a token of a covenant" (ib. 17:11); "And My covenant shall be in your flesh" (ib. 17:13); "for an everlasting covenant" (ib. 17:13); "he hath broken my covenant" (ib. 17:14); "And I will establish My covenant with him" (ib. 17:19); "for an everlasting covenant" (ib. 17:19); "But My covenant I will establish with Isaac" (ib. 17:21).