Genesis 21:1

The Lord visited Sarah - That is, God fulfilled his promise to Sarah by giving her, at the advanced age of ninety, power to conceive and bring forth a son.

Isaac is born according to promise, and grows to be weaned. "The Lord had visited Sarah." It is possible that this event may have occurred before the patriarchal pair arrived in Gerar. To visit, is to draw near to a person for the purpose of either chastising or conferring a favor. The Lord had been faithful to his gracious promise to Sarah. "He did as he had spoken." The object of the visit was accomplished. In due time she bears a son, whom Abraham, in accordance with the divine command, calls Isaac, and circumcises on the eighth day. Abraham was now a hundred years old, and therefore Isaac was born thirty years after the call. Sarah expressed her grateful wonder in two somewhat poetic strains. The first, consisting of two sentences, turns on the word laugh. This is no longer the laugh of delight mingled with doubt, but that of wonder and joy at the power of the Lord overcoming the impotence of the aged mother. The second strain of three sentences turns upon the object of this admiring joy. The event that nobody ever expected to hear announced to Abraham, has nevertheless taken place; "for I have borne him a son in his old age." The time of weaning, the second step of the child to individual existence, at length arrives, and the household of Abraham make merry, as was wont, on the festive occasion. The infant was usually weaned in the second or third year 1 Samuel 1:22-24; 2 Chronicles 31:16. The child seems to have remained for the first five years under the special care of the mother Leviticus 27:6. The son then came under the management of the father.