When Abraham heard God say that he and Sarah would have a child he fell on his face and laughed, he couldn’t help it, this was ridicules. Abraham doubted God and the laughing came from his heart and he suggested that Ishmael could be the one. But God said that Sarah was the one and she would have a son and God told Abraham to call him Isaac. Isaac means laughter and every time Isaac was mentioned Abraham would remember that he doubted God, and Isaac when he grew up would ask, why am I called laughter.
God also promised that Ishmael would be prosperous and be the father of a great people coming from his twelve sons. Ishmael means God hears, and everyday Abraham an all the people in his camp, by the names Isaac and Ishmael, would be reminded that God acts in spite of doubt and that He always hears everyone, He makes no difference.