Genesis 9:14-15

"Whenever I bring clouds over the earth and the rainbow appears in the clouds, I will remember my covenant between me and you and all living creatures of every kind.  Never again will the waters become a flood to destroy all life."  Genesis 9:14-15

In the previous verses God told Noah that he was making a promise to mankind and all the creatures and all the future generations, and now he is telling what that pledge is - he will never again destroy all living creatures and people with flood waters.  The rainbow in the sky reminds both us and God of his promise.  And this is a promise he has kept, no matter how displeasing we are or how much our world rejects him, God has not brought forth another flood.