He was circumcised as a sign of the covenant God had made with him. It showed that his faith had made him right with God before he was circumcised. So Abraham is the father of all believers who have not been circumcised. God accepts their faith. So their faith makes them right with him.
Abraham fell with his face to the ground. He laughed and said to himself,“ Can a 100- year- old man have a son? Can Sarah have a child at the age of 90?”
Abraham did not become weak in his faith. He accepted the fact that he was past the time when he could have children. At that time Abraham was about 100 years old. He also realized that Sarah was too old to have children.But Abraham kept believing in God’s promise. He became strong in his faith. He gave glory to God.