18 And Abraham said to God, Oh that Ishmael might live before thee! 19 And God said, Sarah thy wife shall indeed bear thee a son; and thou shalt call his name Isaac; and I will establish my covenant with him, for an everlasting covenant for his seed after him. 20 And for Ishmael I have heard thee: behold, I will bless him, and will make him fruitful, and will very greatly multiply him; twelve princes shall he beget, and I will make him a great nation. 21 But my covenant will I establish with Isaac, whom Sarah shall bear to thee at this appointed time in the 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.