After Noah's Ark flood, God set a rainbow as the sign of the covenant with Noah.
Genesis 9:12–17 describes the covenant made with Noah, his descendants, and every living creature after the waters receded. The rainbow in the clouds would remind God of the promise never again to destroy all life with a flood.
The passage gives the rainbow a theological meaning within the story. It is presented as a visible sign of a universal promise involving humans and animals, not merely as a private sign for Noah's family.
In modern science, a rainbow forms when sunlight is refracted, internally reflected, and dispersed by water droplets. That physical explanation does not alter the biblical narrative's symbolic use of the phenomenon. The rainbow is distinct from the dove and olive leaf, which signal returning land and peace.