You can’t see a rainbow when you are under a layer of water.
Now that the flood has passed, we have a rainbow as an assurance that God will not flood us out again. The waters above are gone: see the rainbow? That’s how you know.
Dearly beloved, physics says we each see our own rainbow. We each have the same promise, but it’s our own promise, and no one can see it for us, and how we see it depends largely on how we look at it.