Explanation posted by Geneva Notes on 2007-01-01 00:00:00
21:2 For Sarah conceived, and bare Abraham a son in his {a} old age, at the set time of which God had spoken to him.
(a) Therefore the miracle was greater.
Explanation posted by John Wesley on 2007-01-01 00:00:00
Sarah conceived - Sarah by faith, received strength to conceive, Heb. xi, 11. God therefore, by promise, gave that strength. Abraham was old, and Sarah old, and both as good as dead, and then the word of God took place.