The Bible tells us the origin and meaning of the rainbow, Gen. 9:12-17.
Gen. 9:13“I set My bow in the cloud, and it shall be for a sign of a covenant between Me and the earth.”
This is not just as natural phenomenon, as we were taught in physical science class, but the sign of the covenant of God to restrain His anger and never destroy all mankind again.
God says this is “My bow.” The glorious colored circle containing either 6, 7 or 8 colors (depending on how one divides it*), is a symbol of the presence of God. It is very uniquely His and a regular reminder of Him to us.
In Ezek. 1:28 a His glory is compared to a rainbow. In Rev. 4:3 a rainbow surrounds His throne in Heaven, and in Rev. 10:1 one of His strong angels isgiven an rainbow to wear as a crown when he came in glory for the Lord.
Yet today we often see the rainbow used in an entirely different way. It is now used as the banner of homosexual identity and the destructive cultural forces and political power that go with their ungodliness. The perversion of the word “gay” was a great loss to our language, but the appropriation of God’s symbol for Himself for us in a promotion evil is one of Satan’s great (temporary) victories. They have turned the symbol of God’s peace into a reminder of why God restrain Himself from catastrophic judgment. Without that covenant, what might He rightly do to us?
*The rainbow actually contains every visible color in a continuum, including infrared and ultraviolet just above and below the visible spectrum.