The Maturing of Humankind

In the aftermath of the Flood, two seemingly opposite extremes were introduced into the world. On the one hand, the earth achieved stability and permanence: after the Flood, G-d swore to never again destroy the world. On the other hand, the human lifespan was drastically shortened: whereas prior to the Flood people lived for almost 1000 years, after the Flood people began to die at a much younger age.

These changes are not unrelated. Together they reflect the change in human potential that was brought about through the Flood—a change that is likewise expressed in the rainbow, the sign of G-d's promise to never again destroy the entire world.5

A rainbow is caused when moisture that rises from the earth catches and refracts the light of the sun. The moisture rising from the earth represents mortal man's contribution to creation—"from below," as it were. Now, the generations prior to the Flood were sustained by G-d's benevolence alone. After the Flood, however, G-d gave humanity the ability to refine the world and make it receptive to G-dliness, whereby the world became capable of "earning its own keep." Therefore, after the Flood, G-d created the rainbow. He caused the rising moisture to be less dense and more receptive of the light of the sun, reflecting the world's new reality—its potential to be elevated and to become receptive to G-dliness.

Accordingly, the extremes described above are really two sides of the same coin. On the one hand, the world now has the ability to earn and, if necessary, restore G-d's desire in its existence—for eternity, just as He is eternal. By the same token, however, the world's existence is now contingent on mortal man's efforts to deserve life—efforts that are inherently limited and finite. Consequently, the average human lifespan is much shorter now than it was before the Flood, when life was granted by G-d's limitless kindness alone.

—Likkutei Sichos, vol. 15, pp. 51-54