John Gills Exposition of the Bible Commentary - Genesis 21:5
And Abraham was an hundred years old when son Isaac was born unto him. So that this was years after his departure from Haran, and coming into the land of Canaan, for then he was seventy five years of age, Genesis 12:4 ; and this exactly agrees with the account of Demetrius, as related by Polyhistor, an Heathen writer F15 Apud Euseb. Praepar. Evangel. l. 9. c. 21. p. 425. , who makes Isaac to be born just twenty five years from Abraham's coming into the land of Canaan, and who must be... read more
Matthew Henry's Complete Commentary - Genesis 21:1-8
Few under the Old Testament were brought into the world with such expectation as Isaac was, not for the sake of any great person eminence at which he was to arrive, but because he was to be, in this very thing, a type of Christ, that seed which the holy God had so long promised and holy men so long expected. In this account of the first days of Isaac we may observe, I. The fulfilling of God's promise in the conception and birth of Isaac, Gen. 21:1, 2. Note, God's providences look best and... read more