The Unexpected Outcome of a Promise

Paul is showing that Abraham is a model of the type of faith we need in order to get the righteousness of God. In the first half of the chapter, Paul shows that righteousness comes by Abraham's faith, not works. Now in the second half, Paul shows that it is not the content of the promise that was made, rather Abraham had faith in the one promising, one who could make what was dead (Abraham's body, Sarah's womb, a sacrificed Isaac) alive.