Look upon the rainbow, and praise him that made it; very beautiful it is in the brightness thereof.
Read Chapter 43
God almighty set the rainbow as a sign between himself and humanity, indicating that he would never again destroy the world with a flood. And this is why the rainbow has the color of both water and fire"in part light blue and in part red"so that it might testify to both judgments, to the one that is to come and to the one that has already taken place, since the world will be burned by fire and was once destroyed by the waters of the flood. For this reason we liken the rainbow to the Scripture of the New and the Old Testaments, since, in a certain way, it encircles the necks of the faithful with two curved parts. On this we read, "He has strung and aimed his bow," and thus he gives a sweet yoke to to the faithful, but for rebels he proclaims himself to be a fearsome weapon. The rainbow is very beautiful in its brilliance, because the sense and intelligence of sacred Scripture are magnificent. "It encircles the heavens with a ring of glory," because it speaks abundantly of the highest things and of the lowest. - "On Ecclesiasticus 9.7"