Genesis 6:5-6

The LORD saw how great man's wickedness on the earth had become, and that every inclination of the thoughts of his heart was only evil all the time. The LORD was grieved that he had made man on the earth, and his heart was filled with pain.

What a condemning verse...every inclination and evil all the time.  God was displeased in the very center of His being.  He was displeased with their unbelief and their wickedness.  And so God sent the flood.

Shouldn't we want to do everything we can to keep from filling God's heart with pain?

Then after the flood God said to Noah.

Genesis 9:11 
I establish my covenant with you: Never again will all life be destroyed by the waters of a flood; never again will there be a flood to destroy the earth.”

What a great illustration of God’s mercy and grace.