You knew he would be faithful to you, and made an agreement with him to give him and his descendants the land of the Canaanites, Hittites, Amorites, Perizzites, Jebusites, and Girgashites. You kept your promise, because you do what is right.
It was actually before he became a Jew by being circumcised, which was a confirmation of his trust in God to make him right. This happened before he was circumcised, so he is the father of everyone who trusts in God and are considered as right by God, even though they may not be circumcised Jews.
For God was in Christ, bringing the world back from hostility to friendship with him, not counting anyone's sins against them, and giving us this message to change his enemies into his friends.