"Whenever." It is something that would happen many times.
# the rainbow is seen
It is not clear who will see the rainbow, but because the covenant is between Yahweh and people, if you need to say who it is who will see the rainbow, it would be best to name both Yahweh and people. This can be translated in active form. AT: "people and I see the rainbow" (See: [[rc://en/ta/man/translate/figs-activepassive]])