And God saw the earth, and behold, it was corrupt, for all flesh had corrupted their way on the earth. - Genesis 6:12
Corruption of Flesh
As man multiplied on the earth, the sons of God had children with the daughters of man, and the Lord saw his wickedness, the continually evil thoughts of his heart, his violence, and the corruption of the earth.
The Lord said, "My Spirit shall not abide in man forever, for he is flesh: his days shall be 120 years."
He found a righteous man in Noah and told him his intentions to wipe the wicked generation from the earth. "I have determined to make an end of all flesh, for the earth is filled with violence through them. Behold, I will destroy them with the earth. ... For behold, I will bring a flood of waters upon the earth to destroy all flesh in which is the breath of life under heaven. Everything that is on the earth shall die."
(Genesis 6)
God used the flood to blot out every living thing. All flesh died that moved on the earth, birds, livestock, beasts, all swarming creatures that swarm on the earth, and all mankind. Only Noah was left, and those who were with him in the ark.
Noah's covenant
God set the rainbow in the clouds as a sign of the covenant that He will never again destroy all flesh with a flood.
God told Noah, "I have set my bow in the cloud, and it shall be a sign of the covenant between me and the earth. When I bring clouds over the earth and the bow is seen in the clouds, I will remember my covenant that is between me and you and every living creature of all flesh. And the waters shall never again become a flood to destroy all flesh. When the bow is in the clouds, I will see it and remember the everlasting covenant between God and every living creature of all flesh that is on the earth.”
(Genesis 9)