John Chrysostom

How was it that he "believed in hope against hope?" It was against man's hope, in hope which is of God. (For he is showing the loftiness of the action, and leaving no room for disbelieving what is said.) Things which are contrary to one another, yet faith blends them together. But if he were speaking about such as were from Ishmael, this language would be superfluous: for it was not by faith but by nature that they were begotten. But he bringeth Isaac also before us. …

Homily on Romans VIII ↗

Theophylact of Ohrid

Do not think, he says, that Abraham was honored without merit. For how could this be, when beyond human hope he believed with divine hope that he would become the father of many nations — not those who descended from Ishmael (for they descended from Abraham not by faith, but by nature), but those who are like him in faith?

Commentary on Romans ↗

Thomas Aquinas

Then when he says who against hope, he commends Abraham's faith. First, he shows the greatness of his faith; second, its efficacy or fruit, at and therefore it was reputed. In regard to the first he does two things: first, he shows the greatness of Abraham's faith as far as the promise of multiplying his descendants is concerned; second, in regard to the promise to exalt his descendants, at in the promise also. …

Commentary on Romans ↗