Abraham serves as an example. He believed God, and that faith was regarded by God to be his approval of Abraham.
You must understand that people who have faith are Abraham's descendants.
Scripture saw ahead of time that God would give his approval to non-Jewish people who have faith. So Scripture announced the Good News to Abraham ahead of time when it said, "Through you all the people of the world will be blessed."
So people who believe are blessed together with Abraham, the man of faith.