God destroyed the earth with a flood because He was grieved/disappointed by man’s evil ways.

He made a promise that He will not destroy the earth with water again.

His promise is The Rainbow!

Genesis 9:11, 13 (KJV) – and I will establish my covenant with you; neither shall all flesh be cut off any more by the waters of a flood; neither shall there any more be a flood to destroy the earth. I do set my bow in the cloud, and it shall be for a token of a covenant between me and the earth.