Comparing the biblical description of the rainbow as a sign of God’s postdiluvian covenant with mankind to understandings of the rainbow in other ancient Near Eastern literature, Ron Hendel argues that the differences speak more loudly than the similarities. Ancient Mesopotamians saw the rainbow, like other celestial phenomena, as a sign that, if properly interpreted by skilled astrologers, could portend divine intentions. In Genesis, by contrast:
God is His own omen interpreter, and the encrypted meaning is meant for Him. This turns upside down the customary system of omens and their interpretation. . .
[It is also noteworthy that] Hebrew uses the word keshet for both a bow as a weapon . . . and for a rainbow; the former meaning is primary. Since the flood story is not about combat, the presence of God’s bow may seem out of place. . . .
[I]n the Mesopotamian creation account, . . . after the warrior-god Marduk uses his mighty bow and arrows to defeat the sea-monster Tiamat, the high god Anu places the bow in heaven as a bright star. . . .
God’s bow in Genesis has a comparable resonance. In the flood story, God triumphs over chaos. But the chaos in the flood story is not the rage of a sea-monster, it is rather the violence of all flesh that has corrupted its ways on earth, and which has, as a consequence, corrupted the earth. The flood is God’s natural agent to cleanse the earth from the violence of bloodshed.
After the waters of the flood have receded, God hangs His bow in the sky, . . . but the bow is not His triumphant weapon. The rainbow is a sign of peace, of God’s promise that the flood will never come again.
Read more on theTorah.com: http://thetorah.com/the-rainbow-in-ancient-context/