What does 'against hope, believed in hope' mean in Romans 4:18?
It means Abraham trusted God's promise even when it contradicted common sense and physical possibility. At a hundred years old, with Sarah ninety, he still held genuine hope that God would give the promised son and make him a father of many nations.
Les explains that 'against hope, believed in hope' means Abraham's faith ran contrary to common sense. Abraham was a hundred years old and his wife was ninety, yet God kept telling him he would have a son and that a nation of people would come from his body. Humanly, according to the physical understanding of reproduction, this seemed ridiculous. But Abraham had genuine hope because he knew God was going to bring it to pass regardless of how impossible it appeared. The surrounding verses show the same God who quickens the dead and calls things that are not as though they were, the God who created out of nothing. That divine prerogative undergirds Abraham's hope, and the promise was fulfilled as he became the father of many nations.
Who against hope believed in hope, that he might become the father of many nations, according to that which was spoken, So shall thy seed be.