When things go wrong, we can either cry or laugh.  God says that a cheerful heart does good like taking medicine.  Medicine helps the body heal.  Laughter gives healing to our body and soul.  When Abraham and Sarah were childless in their old age, it became difficult to believe the promise God gave them that they would have many children.  Their child bearing years were over!  But God delivered His promise in Isaac.  When Sarah heard that she would have a baby at her ripe, old age, she laughed and laughed.  Isaac means laughter.  God is able to perform His promises and bring laughter into our hearts as well.