John Calvin Commentary Genesis 9:13

"I do set my bow in the cloud, and it shall be for a token of a covenant between me and the earth." — Genesis 9:13 (ASV)

I do set my bow in the cloud. From these words, certain eminent theologians have been induced to deny that there was any rainbow before the deluge, which is frivolous. For the words of Moses do not signify that a bow was then formed which did not previously exist, but that a mark was engraved upon it, which should give a sign of divine favor towards men.

To make this appear more evidently, it is well to recall what we have said elsewhere: that some signs are natural, and some preternatural. And although there are many examples of this second class of signs in the Scriptures, yet they are distinct and do not belong to the common and perpetual use of the Church.

For, as it pleases the Lord to use earthly elements as vehicles for raising men’s minds on high, so I think the celestial arch, which had previously existed naturally, is here consecrated as a sign and pledge; thus, a new office is assigned to it. Whereas, from the nature of the thing itself, it might rather be a sign of the contrary, for it threatens continued rain.

Let this, therefore, be the meaning of the words: ‘As often as the rain alarms you, look upon the bow. For although it may seem to cause the rain to overflow the earth, it will nevertheless be to you a pledge of returning dryness, and thus it will then be appropriate for you to stand with greater confidence than under a clear and serene sky.’

Hence, it is not for us to contend with philosophers concerning the rainbow. For although its colors are the effect of natural causes, yet those who attempt to deprive God of the right and authority he has over his creatures act profanely.