Abraham was circumcised later to show that God accepted him. His circumcision was proof 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. They believe and are accepted as people who are right with God.
Abraham bowed his face to the ground to show he respected God. But he laughed and said to himself, “I am 100 years old. I cannot have a son, and Sarah is 90 years old. She cannot have a child.”