A rainbow is a promise. God our Father reaffirmed the promise He made about our Redemption in the Garden of Eden when Noah landed on the rock after having spent forty days and forty nights in the ark during the flood. The Lord stopped the rain, and gave us a double rainbow.
"God said: `Here is the sign of the Covenant I make between Myself and every living creature with you for all generations; I set My bow in the clouds and it shall be a sign of the Covenant between Myself and you and every living creature of every kind."
Our Lord Jesus fulfilled the promise that God the Father made. As he committed to St. Dismas, the good thief, from the Cross, He also pledges to us:
"Indeed, I promise you, this day you will be with Me in Paradise."
We believe that when we die, when we shake off this mortal coil, we go to the next step in our eternal existence, from a physical, bodily life, to a new life, a new beginning.