Genesis 9:13

I have set My Bow in the cloud, and it shall be for a token of the covenant between My Word and the earth.

My bow: Behold, I have put my bow in the cloud now. And it's interpretation is not, as the Ga'on said, that it was there from the beginning.

את קשתי נתתי בענן, I have arranged that the rainbow become a natural phenomenon.

והיתה לאות ברית, there is a dual function to the rainbow; it is true that the scientists have already tired of trying to explain the phenomenon of the various colours of the second rainbow, something which appears in the opposite order of the colours in the original rainbow, [according to the encyclopedia Britannica, there are primary and secondary rainbows, the secondary rainbow having a colour pattern in a reverse order of that known as the primary rainbow. Our author may understand that which has baffled scientists in his time, as a hint of the dual nature of the rainbow, i.e. as a warning, or a promise respectively. Ed.] According to the view of the sages in Ketuvot 77 the very appearance of the rainbow is a reminder that the generation in which it appears is a guilty generation. It is reported there that two generations were fortunate enough that in their time no rainbow was ever observed. This was interpreted as a sign that the people of that generation did not need the phenomenon of the rainbow to alert them to become penitents. Their religious leaders did an outstanding job in prevailing on the people to be Torah-observant. [according to the של'ה, it is not reasonable to assume that there were periods when the laws of nature were suspended and there was no rainbow; rather if the Jewish people during certain periods were very deserving, had lots of merits, so that they did not need to be reminded of the deluge, the rain descended at night when no rainbow would become visible even if they had not been a deserving generation. Ed.]

את קשתי נתתי בענן, the reason why G’d speaks of “My” rainbow, instead of “the rainbow,” is because He had now made it the visible reminder of the covenant between Himself and mankind, just as He had said ביני ובין הארץ, “between Me and the earth,” or as the prophet Ezekiel refers to this in Ezekiel 1,28 כמראה הקשת, “as the manifestation of the rainbow.” The prophet considered the vision he had seen in that chapter as comparable to the spectacle of the rainbow, i.e. something of which he stood in awe. Concerning this the question is raised in Bereshit Rabbah 35,3 that the word קשתי means מוקש לי, “an hidden obstacle for Me, a stumbling block for Me., [If I understand this correctly, the problem is if the rainbow as a reminder is supposed to frighten man into conducting himself properly so that no deluge will be necessary, or if he is to think only of the promise that there will not be another flood, just as now after the rain the sunlight appears in many different colours, something beautiful and certainly encouraging. Ed] Nowadays, the emphasis is only on the promise, as we have never experienced a deluge, unlike the sons of Noach for whom each time a rainbow appeared it reminded them of the horrible ordeal from which they had been saved.