Verse 7. - And she said, Who would have said unto Abraham, - מִלֶּל, the poetic word for דּבֵּר, is introduced by מִי in order to express astonishment; the meaning being that what had happened was altogether out of the ordinary course of nature, was, in fact, God's work alone (Vatablus, Calvin, Rosenmüller, Keil, Kalisch, 'Speaker's Commentary'). Less happy are τίς ἀναγγελεῖ τῳ Ἀβραὰμ (LXX.); quis auditurum crederet Abraham quod (Vulgate); quam fidelis est ille qui dixit Abrahamo (Onkelos) - that Sarah should have given children suck? Literally, Sarah suckleth sons. "Many of the greatest saints in Holy Scripture, and even our Lord himself, were nursed by their own mothers" (Wordsworth). For I have born him a son in his old age. Literally, I have born a son to his old age. The LXX. incorrectly render ἐν τῶ γήρᾳ μου.

21:1-8 Few under the Old Testament were brought into the world with such expectations as Isaac. He was in this a type of Christ, that Seed which the holy God so long promised, and holy men so long expected. He was born according to the promise, at the set time of which God had spoken. God's promised mercies will certainly come at the time which He sets, and that is the best time. Isaac means laughter, and there was good reason for the name, ch. 17:17; 18:13. When the Sun of comfort is risen upon the soul, it is good to remember how welcome the dawning of the day was. When Sarah received the promise, she laughed with distrust and doubt. When God gives us the mercies we began to despair of, we ought to remember with sorrow and shame our sinful distrust of his power and promise, when we were in pursuit of them. This mercy filled Sarah with joy and wonder. God's favours to his covenant people are such as surpass their own and others' thoughts and expectations: who could imagine that he should do so much for those that deserve so little, nay, for those that deserve so ill? Who would have said that God should send his Son to die for us, his Spirit to make us holy, his angels to attend us? Who would have said that such great sins should be pardoned, such mean services accepted, and such worthless worms taken into covenant? A short account of Isaac's infancy is given. God's blessing upon the nursing of children, and the preservation of them through the perils of the infant age, are to be acknowledged as signal instances of the care and tenderness of the Divine providence. See Ps 22:9,10; Ho 11:1,2.And she said, who would have said unto Abraham,.... No one a year ago could ever have thought of such a thing, much less have come and told Abraham that he should have a child or children by Sarah; the thing was incredible, and next to impossible; none but God himself, or an angel from him, could have declared this, as none but he could bring it about, the thing is so marvellous and astonishing:

that Sarah should have given children suck? that she who was ninety years of age should bear a child, and suckle it, as she did; and in doing which she set an example to her daughters to do the like, since neither age nor grandeur, nor the business of her family, were any objection to this duty of nature; and her being able to do this was a clear proof that this was truly a child of her own. The plural number may be put for the singular, as it often is, see Genesis 46:23; or Sarah might think, as she had strength given her to bear and suckle one child, she might bear and suckle more; though the phrase seems only to be expressive and descriptive of her as a nursing mother:

for I have borne him a son in his old age; See Gill on Genesis 21:2.