Берешит 17:4 Галаха: Mishneh Torah, Circumcision & Sefer HaChinukh

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).

And they, may their memory be blessed, also said (Mishnah Bikkurim 1:4) about this matter that converts bring them and recite, even though the land was not distributed to them. As it was given to Avraham first, and he was called “the father of many nations” (Genesis 17:4) — meaning to say that anyone who converts is considered like his son.