Genesis 25:26

Isaac was threescore years old, &c.— It has been asked, why God permitted Sarah and Rebekah to continue so long barren? To which it is answered, not only to prove and exercise the faith of these patriarchs, but to render the propagation of the blessed Seed more remarkable. It prepared the way for the coming of the Son of God in the flesh, and, as St. Chrysostom expresses it, predisposed the world to the belief of the miraculous conception of the Blessed Virgin.