That is true. But those branches were broken off because they did not believe, and you continue to be part of the tree only because you believe. Do not be proud, but be afraid.
So do we have a reason to brag about ourselves? No! And why not? It is the way of faith that stops all bragging, not the way of trying to obey the law.
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.