Gen 17:13

17:13 born . . . bought. The covenant promises were extended to all within the household of faith. Even in the Old Testament, the scope of the covenant community was not exclusively determined by ancestry—a foreshadowing of the expansion of the covenant to a multitude from every tribe and nation. See notes on vv. 6, 7.

in your flesh an everlasting covenant. See note on v. 7. The covenant of grace between God and His people is indeed an eternal covenant, although the mode of administration changes with the transition from Israel to the church (e.g., circumcision is replaced by baptism, v. 12 note). See “The Sacraments” at Matt. 28:19.