18 And Abraham said to God, "O that Ish'mael might live in thy sight!" 19 God said, "No, but Sarah your wife shall bear you a son, and you shall call his name Isaac. I will establish my covenant with him as an everlasting covenant for his descendants after him. 20 As for Ish'mael, I have heard you; behold, I will bless him and make him fruitful and multiply him exceedingly; he shall be the father of twelve princes, and I will make him a great nation. 21 But I will establish my covenant with Isaac, whom Sarah shall bear to you at this season next year."
Matthew Henry's Commentary on Genesis 17:18-21
Commentary on Genesis 17:15-22
(Read Genesis 17:15-22)
Here is the promise made to Abraham of a son by Sarai, in whom the promise made to him should be fulfilled. The assurance of this promise was the change of Sarai's name into Sarah. Sarai signifies my princess, as if her honour were confined to one family only; Sarah signifies a princess. The more favours God confers upon us, the more low we should be in our own eyes. Abraham showed great joy; he laughed, it was a laughter of delight, not of distrust. Now it was that Abraham rejoiced to see Christ's day; now he saw it and was glad, John 8:56. Abraham, dreading lest Ishmael should be abandoned and forsaken of God, put up a petition on his behalf. God gives us leave in prayer to be particular in making known our requests. Whatever is our care and fear, should be spread before God in prayer. It is the duty of parents to pray for their children, and the great thing we should desire is, that they may be kept in covenant with Him, and may have grace to walk before him in uprightness. Common blessings are secured to Ishmael. Outward good things are often given to those children of godly parents who are born after the flesh, for their parents' sake. Covenant blessings are reserved for Isaac, and appropriated to him.