John Chrysostom

Do you see how he gives the obstacles, as well as the high spirit of the righteous man which surmounts all? "Against hope," he says, was that which was promised: this is the first obstacle. For Abraham had no other person who had received a son in this way to look to. They that were after him looked to him, but he to no one, save to God only. And this is why he said, "against hope." Then, "his body now dead." This is a second. And, "the deadness of Sarah's womb." This is a third, aye and a fourth obstacle.

Homily on Romans VIII ↗

Theophylact of Ohrid

Having said that Abraham beyond human hope believed with the hope of God, he now proves this, saying that Abraham was told: "I will multiply your seed as the stars of heaven and as the sand" (Gen. 15:5, 22:17); yet he did not weaken in faith, but, remaining firm in it, paid no attention either to his own body, already deadened by time, or to the double deadening of Sarah's womb (for her womb was deadened both by old age and by barrenness), and did not fall into perplexity, that is, he did not doubt in the least, was not shaken in …

Commentary on Romans ↗

Thomas Aquinas

Then when he says, and he was not weak, he shows Abraham's firmness. For as temperance is shown not to be weak, because it is not overcome by strong temptations, so faith is shown not to be weak but strong, because it is not overcome by great difficulties: resist him, firm in your faith (1 Pet 5:9). Second, at neither did he consider, he mentions the difficulties from which it is shown that his faith was not weak. …

Commentary on Romans ↗