“That is why it depends on faith, in order that the promise may rest on grace and be guaranteed to all his offspring …” (v16). If the promise of blessing (all the good that flows from a relationship with God) rested on the law, we would have no hope, because “the law brings wrath” (v15). A contract based on our obedience would certainly end in our punishment. Instead, our faith rests on grace, the freely-given love of God, “who gives life to the dead and calls into existence the things that do not exist” (v17).
Abraham’s faith meant a decision to put his life in God’s hands, “fully convinced that God was able to do what He had promised” (v21).