Albert Barnes Commentary Romans 4:18

"Who in hope believed against hope, to the end that he might become a father of many nations, according to that which had been spoken, So shall thy seed be." — Romans 4:18 (ASV)

Who against hope. That is, who, contrary to all apparent or usual grounds for hope. He refers here to the prospect of posterity. See Romans 4:19-21.

Believed in hope. He believed in what was promised, which was intended to inspire his hope. Hope here represents the object of his hope—that which was promised.

According to that which was spoken (Genesis 15:5).

So shall thy seed be. That is, as numerous as the stars in heaven. Your posterity shall be very numerous.