19 And being not weak in faith, he considered not his own body now dead, when he was about an hundred years old, neither yet the deadness of Sara's womb:
This may be understood literally or figuratively. In the literal sense, Abraham did not put his trust in his hundred-year-old body, which was obviously incapable of doing what God had promised him, but rather he trusted in God, the Almighty One who could perform what he had promised even when the laws of human fertility no longer functioned.… Figuratively, however, it may be understood in the light of what Paul says elsewhere: “Put to death therefore what is earthly in you.” It would be absurd to suggest that what Paul had in this respect was somehow lacking to Abraham. For Abraham also had put his earthly members to death, being neither excited by luxury nor inflamed by lust.… Sarah likewise did not suffer from lust or the desires of the flesh.… When they heard what God had promised them, they did not consider their own benefit.… All these things that would make them rich they regarded as worthless in order that they might win Christ, whose coming they foresaw.
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.
[AD 253] Origen of Alexandria on Romans 4:19