God, Paul said in Romans 4:17, brought life out of the dead. What does this look like in real life? While the focus of 4:17 seems to be on Gentiles, that life-giving-faith is at the heart of the Jewish family because it is the faith of Abraham.
Romans 4:18-22 shows how Abraham’s life-giving-faith is the faith that gave rise even to Israel’s own faith. And in short, Abe’s faith was that God would give Sarah and him a baby in spite of their age. They are both old, too old.

But Abraham believed “in hope against hope.”
Why, he believed the God he was trusting that God “had power to do what he had promised.”
This is the faith that was reckoned to Abraham as righteousness.
I’m impressed by the concrete reality of Abraham’s faith, and of Paul’s understanding of Abraham’s faith.
I’m also impressed that Paul will connect, in the verses that follow, this kind of faith to faith in the God who raised Jesus from the dead. Abraham’s faith is resurrection faith.
Wright has a magnificent chart comparing Abraham’s faith here with the collapse of humans in Romans 1 — words like glory, creator, God’s power, and the proper joining of man and woman — and this shows that Paul is showing Abraham as acting as all humans are to act.