Romans 4:11-13, 16

Abraham was circumcised to show that he was right with God through faith before he was circumcised. So Abraham is the father of all those who believe but are not circumcised; he is the father of all believers who are accepted as being right with God. And Abraham is also the father of those who have been circumcised and who live following the faith that our father Abraham had before he was circumcised. Abraham and his descendants received the promise that they would get the whole world. He did not receive that promise through the law, but through being right with God by his faith.

So people receive God’s promise by having faith. This happens so the promise can be a free gift. Then all of Abraham’s children can have that promise. It is not only for those who live under the law of Moses but for anyone who lives with faith like that of Abraham, who is the father of us all.