15 And God saith unto Abraham, 'Sarai thy wife—thou dost not call her name Sarai, for Sarah 'is' her name; 16 and I have blessed her, and have also given to thee a son from her; and I have blessed her, and she hath become nations—kings of peoples are from her.' 17 And Abraham falleth upon his face, and laugheth, and saith in his heart, 'To the son of an hundred years is one born? or doth Sarah—daughter of ninety years—bear?' 18 And Abraham saith unto God, 'O that Ishmael may live before Thee;' 19 and God saith, 'Sarah thy wife is certainly bearing a son to thee, and thou hast called his name Isaac, and I have established My covenant with him, for a covenant age-during, to his seed after him. 20 As to Ishmael, I have heard thee; lo, I have blessed him, and made him fruitful, and multiplied him, very exceedingly; twelve princes doth he beget, and I have made him become a great nation; 21 and My covenant I establish with Isaac, whom Sarah doth bear to thee at this appointed time in the next year;' 22 and He finisheth speaking with him, and God goeth up from Abraham.
Matthew Henry's Commentary on Genesis 17:15-22
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.