God promised Abraham that his descendants would be great. (Genesis 12:2, 17:4) Abraham was getting older and wondering if this promise was really going to happen. When God again made this promise to Abraham (17:16), he laughed and questioned to himself how this could happen to a man who was a hundred years old and a woman who was ninety. (17:17) Sarah also laughed when she heard this promise. (18:12) God works in ways we sometimes do not understand, but he always keeps his promises.