Following the flood, God made a promise never to destroy all flesh via a flood. We find that promise recorded in Gen 9:9-17 (NASB):
“Now behold, I Myself do establish My covenant with you, and with your descendants after you; (10) and with every living creature that is with you, the birds, the cattle, and every beast of the earth with you; of all that comes out of the ark, even every beast of the earth. (11) I establish My covenant with you; and all flesh shall never again be cut off by the water of the flood, neither shall there again be a flood to destroy the earth. (12) God said, ‘This is the sign of the covenant which I am making between Me and you and every living creature that is with you, for all successive generations; (13) I set My bow in the cloud, and it shall be for a sign of a covenant between Me and the earth. (14) It shall come about, when I bring a cloud over the earth, that the bow will be seen in the cloud, (15) and I will remember My covenant, which is between Me and you and every living creature of all flesh; and never again shall the water become a flood to destroy all flesh. (16) When the bow is in the cloud, then I will look upon it, to remember the everlasting covenant between God and every living creature of all flesh that is on the earth.’ (17) And God said to Noah, ‘This is the sign of the covenant which I have established between Me and all flesh that is on the earth.'”
The rainbow is a sign of God’s covenant never to bring another flood to destroy all flesh.
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