According to Genesis, a rainbow was the sign of God’s covenant with Noah.
Genesis 9:12–17 presents the rainbow in the clouds as the sign of a covenant between God, Noah, and every living creature after the Flood. The covenant promises that a flood will not again destroy all life on Earth, and the rainbow serves as its visible reminder.
The passage gives the sign a universal scope: it is not limited to Noah’s family but is linked with living creatures and future generations. In the narrative, the rainbow appears after Noah leaves the Ark and after he builds an altar.
The biblical account does not claim that rainbows first began to exist at this moment. Instead, it assigns the natural phenomenon a covenantal meaning within the story. That distinction helps avoid a common confusion between the physical formation of rainbows and their symbolic role in Genesis.