Genesis 17:4 - Joseph Benson’s Commentary on the Old and New Testaments

The promise is here introduced with solemnity: As for me, saith the great God, behold Admire, and be assured of it; my covenant is with thee; and thou shalt be a father of many nations This implies, 1st, That his seed after the flesh should be very numerous, both in Isaac and in Ishmael, and in the sons of Keturah. And the event answered; for there have been, and are, more of the children of men descended from Abraham, than from any one man at an equal distance with him from Noah, the common root. 2d, That all believers in every age should be looked upon as his spiritual seed. In this sense the apostle directs us to understand this promise, Romans 4:16. He is the father of the faithful, of those, in every nation, that, by faith, enter into covenant with God, and (as the Jewish writers express it) are gathered under the wings of the Divine Majesty.