God gave Noah a rainbow as the sign of the post-Flood covenant.
Genesis 9:13 says God set the rainbow in the cloud as a sign of the covenant between God, Noah, and every living creature. The covenant follows the Flood and includes the promise that waters would not again become a flood to destroy all life.
In Genesis, the rainbow is presented as a visible reminder of that promise. The passage repeats that when the rainbow appears in the cloud, God will remember the everlasting covenant between God and every living creature on earth.
The rainbow’s scientific explanation is separate from its biblical symbolism. In nature, rainbows result when light is refracted, reflected, and dispersed by water droplets. Genesis uses the familiar atmospheric phenomenon within its theological account of the Flood and its aftermath.