211 And the Lord visited Sarah as He had said, and the Lord did for Sarah as He had spoken. 2 For Sarah conceived and bore Abraham a son in his old age, at the set time of which God had spoken to him. 3 And Abraham called the name of his son who was born to him--whom Sarah bore to him--Isaac. 4 Then Abraham circumcised his son Isaac when he was eight days old, as God had commanded him. 5 Now Abraham was one hundred years old when his son Isaac was born to him. 6 And Sarah said, "God has made me laugh, and all who hear will laugh with me." 7 She also said, "Who would have said to Abraham that Sarah would nurse children? For I have borne him a son in his old age."
Matthew Henry's Commentary on Genesis 21:1-7
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.