God's promise is Received through faith Romans 4:13

13 When God promised Abraham and his descendants that the world would belong to him, he did so, not because he believed and was accepted as righteous by God. 14 For if what God promise is to be given to those who obey the law, then faith means nothing and God's promise is worthless. 15 The law brings down God's anger; but where there is no law there is no disobeying of the law. 16 And so the promise was based on faith, in other that the promise should be guaranteed as God's free gift to all of Abraham's descendants -- not just to those who obey the law, but also to those who obey the law, but also to those who believes as Abraham did for Abraham is the spiritual father of us all?