Parashah Noach

"I have placed My (rain)bow in the cloud…" [9:13] 
From the perspective of Kabbalah, the word keshti (my bow) is derived from kasha (hard, severe). It is a reference to the attribute of Justice, the "hard" attribute. G-d said that it should become the sign of the covenant, i.e., the sign of circumcision. The Torah very significantly did not say "the rainbow I have placed in the cloud," in other words "the well known rainbow." The reason G-d refers to "My rainbow," is to remind us that the cloud He speaks of is not one of the regular clouds that appear in the sky every day. He does not speak of the kind of cloud which discharges rain. G-d speaks of the ananeih hakovod (the clouds of glory) such as when we are told in Exodus 16:10 "and behold! The glory of G-d became manifest in the clouds" (the prelude to the Israelites receiving meat and bread from heaven at the hands of G-d.) The meaning of the words in our verse "and the bow could be seen in the clouds" is "the attribute of Justice will (then) become manifest in the cloud." Seeing that we have a verse in Ezekiel 1:28 "as the appearance of the bow which shall be on a rainy day, so was the appearance of the brilliance all around. That was the appearance of the semblance of the glory of G-d" Our sages in Chagigah 16 interpreted these words as being a warning that anyone who looks deliberately at the rainbow will have diminished eyesight.
You should be enlightened by the following comment in Bereishit Rabbah 35:3 on the words "I have placed My (rain)bow in the cloud…" "The word keshti describes something that is an obstacle for Me." Is there then such a thing as an "obstacle"
for G-d? Is there anything that HE cannot overcome? We must therefore understand the word as derived from kash (straw) the pedicle of a fruit. Why did the Midrash repeat the same comment twice? Look at the conclusion of the passage! Here
G-d speaks to Noach alone (not to his children) when He says "this is the sign of the covenant which I have established between Me and all of mankind." At this point G-d took Noach into His confidence and revealed a mystical aspect to him that He had not revealed to his children. This is the deeper meaning of the words, "this is the sign (visible symbol) of the covenant." [Gen.9:17]

Bachya - credits
Selected with permission from the seven-volume English edition of The Torah Commentary of Rebbeinu Bachya, as translated and annotated by Eliyahu Munk. Rabbi Bachya ben Asher [1255-1340] of Saragosa, Spain, was the outstanding pupil of Rabbi Shlomo ben Aderet (the "Rashba"), a main disciple of Rabbi Moshe ben Nachman (the "Ramban"). Several books have been written about the Kabballah-based portions of R. Bachya's commentary.