According to the Biblical mythology a rainbow is a sign of the Covenant (promise) made by God to Noah after the massive deluge that had destroyed every living thing on earth, that there would be no such deluge again.
"For ever since the world was created, people have seen the earth and the sky. Through everything God made, they can clearly see his invisible qualities- his eternal power and divine nature. So they have no excuse for not knowing God.
Heaven On Earth, Cloud Atlas, Ice Crystals, Lenticular Clouds, God, Beautiful, Mother Nature, Heavens, The Clouds