I thought about God's promise after the flood to never destroy the earth again, and how the sign of the promise was to be the rainbow in the sky. This always puzzled me. We know that rainbows are formed by the refraction of light through water; certainly light and water existed before that time. Even without rain, you can sometimes see a rainbow in mists.
I don't think the sign was specifically created for the promise; rather, the sign existed already and was appropriated because of it's relevance to the promise. Its relevance to God's promise to never destroy the earth again by flood is obvious in one way--rainbows appear after a rainstorm.
But it is also relevant in another way. Just as sure as a rainbow follows a rainstorm, so God will keep His promises. I think this is the core meaning of the rainbow as a sign. Just as sure as the laws of nature operate, is that God will do what He says.
In this passage, God also promised the inverse. For He said, as long as the earth exists, that seasons, weather, and the rising and setting of the sun will continue. In this, we see that while the laws of nature are sure and firmly consistent, this only matches the consistency of God because God has made it so in creating those laws.
One is reminded of Christ's reminder to Pontius Pilate, that he would have no power except it were given to him from above. As the hymn says, "naught have I gotten, but what I've received." Truly we are blessed beneficiaries of the Lord Who is the Giver of all things.
Blessed be the Lord, Who daily loads us with benefits, The God of our salvation! Selah.