211 And the Lord came to Sarah as he had said and did to her as he had undertaken. 2 And Sarah became with child, and gave Abraham a son when he was old, at the time named by God. 3 And Abraham gave to his son, to whom Sarah had given birth, the name Isaac. 4 And when his son Isaac was eight days old, Abraham made him undergo circumcision, as God had said to him. 5 Now Abraham was a hundred years old when the birth of Isaac took place. 6 And Sarah said, God has given me cause for laughing, and everyone who has news of it will be laughing with me. 7 And she said, Who would have said to Abraham that Sarah would have a child at her breast? for see, I have given him a son now when he is old.
8 And when the child was old enough to be taken from the breast, Abraham made a great feast.
Matthew Henry's Commentary on Genesis 21:1-8
Commentary on Genesis 21:1-8
(Read Genesis 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, Psalm 22:9,10; Hosea 11:1,2.