Matthew Henry on Genesis 17:7-14

The covenant of grace is from everlasting in the counsels of it, and to everlasting in the consequences of it. The token of the covenant was circumcision. It is here said to be the covenant which Abraham and his seed must keep. Those who will have the Lord to be to them a God, must resolve to be to him a people. Not only Abraham and Isaac, and his posterity by Isaac, were to be circumcised, but also Ishmael and the bond-servants. It sealed not only the covenant of the land of Canaan to Isaac's posterity, but of heaven, through Christ, to the whole church of God. The outward sign is for the visible church; the inward seal of the Spirit is peculiar to those whom God knows to be believers, and he alone can know them. The religious observance of this institution was required, under a very severe penalty. It is dangerous to make light of Divine institutions, and to live in the neglect of them. The covenant in question was one that involved great blessings for the world in all future ages. Even the blessedness of Abraham himself, and all the rewards conferred upon him, were for Christ's sake. Abraham was justified, as we have seen, not by his own righteousness, but by faith in the promised Messiah.