Matthew Poole and continuators on Genesis 17:21

21 But my covenant will I establish with Isaac whom Sarah shall bear unto thee, at this set time, in the next year.

The Covenant of the promised Seed to come out of his Loins, and of Life and Salvation to accrue to himself and to his posterity by vertue of that Seed: In comparison whereof God speaks slightly of all the Temporal blessings conferred upon Ishmael, though in themselves they were great and glorious. By which it may sufficiently appear that Abrahams Faith whereby he is said to be justified Rom. 4. Had a farther reach in it than to his own immediate Child, even to the Messias, whose Day therefore Abraham is said to have seen, Ioh. 8. 56.