First, let’s clear up a misconception. Although many see the rainbow as a beautiful symbol of peace, its biblical origin is not all that positive. Let’s take a look.

The Basic Story

After years of watching the moral decay of civilization, G‑d had had enough. He brought about the Great Flood, from which only Noah and his family were saved by entering the ark. After the water subsided, Noah left the ark and brought sacrifices to G‑d. G‑d then made a covenant with Noah and his descendants (i.e., all of mankind) that He would never again bring forth a flood to destroy all of civilization. G‑d then said:

This is the sign I am making, testifying to the covenant between Me and you and all living souls, forever: I have put my rainbow in the clouds, and it will be the sign of the covenant between Myself and the world. When I send clouds over the earth, the rainbow will be seen in the clouds, and I will remember the covenant between Myself and yourselves and all living souls, and there will never again be a flood to destroy all life. The rainbow will be in the clouds and I will see it and remember the eternal covenant between G‑d and all the living souls on earth.1

The rainbow is a sign that despite the fact that mankind is sinning and may deserve another deluge, G‑d remembers His promise. Thus, it is considered a very positive sign when no rainbow is seen for an extended period of time, since it implies that we are not sinning and not deserving of a flood.2

Now let’s address the question of why, of all phenomena, G‑d chose the rainbow to signify His oath not to destroy the world.

The King in All His Glory

The Divine Glory is compared to the appearance of the rainbow. In the words of the prophet Ezekiel, “Like the appearance of the rainbow that is in the cloud on a rainy day, so was the appearance of the brightness round about; that was the appearance of the likeness of the glory of the L‑rd´. . .”3

When a mortal king is angry, he hides from his people. Thus, through showing us a rainbow (His image, as it were), G‑d is saying, “If it were My intention to destroy you, I would not first show you a semblance of My glory.”4

A Reversed Bow

Nachmanides points out that the rainbow is like a bow pointing upward, trained toward the heavens. When warriors want to show that they have peaceful intentions, they reverse their weapons away from those in front of them and point the weapons toward themselves. So too, G‑d turns His “bow,” the rainbow, away from humanity and towards the heavens, demonstrating that He will not use the weapon of water to destroy civilization again.5

Rain Tapering Off

The rainbow is only seen in the sky once the rain tapers off or stops altogether. Thus, the rainbow is a sign that any rain will eventually stop and there will not be a flood like in the days of Noah.6

Fire and Water

A rainbow is formed due to the combination of both fire (light) and water. Thus, the rainbow symbolizes peace, harmony and positive synergy.7

The Ability to Refine the World

You may now be wondering whether the rainbow existed before the Flood. Some commentaries explain that although in theory the rainbow could have appeared before the Flood, the clouds were much thicker then and rainbows were never actually seen. It was only after the Flood that G‑d refined the atmosphere and rainbows became visible.8 (Learn more: What Is the Significance of the Rainbow?)

The Lubavitcher Rebbe explains that the physical is a reflection of the spiritual. Before the Flood, the clouds—which are formed by the mist that rises from the ground—were thicker because the world in general was more coarse. After the Flood, the clouds became more refined and one could see a rainbow, a sign that man now had the ability to refine the coarse materiality of the world.9

It is no wonder that the Zohar states that “one should not expect the coming of Moshiach until the rainbow is seen . . . in shining colors."10

May it be speedily in our days!