The mitzvah of the sabbatical year allows the land to rest and replenish itself every seven years. Lest one be concerned, "What will we eat in the seventh year" the Torah tells us that "the sixth year will give three years' worth of bounty."
But if the land is so depleted in the sixth year that it needs to rest, how can the sixth year produce three years' worth of food?
To understand this paradox, we look at another paradox, the fact that there was a college campus where the Chabad House stopped serving matzo ball soup because the kids didn't know what it was.
Based on Likkutei Sichos, vol. 27, pp. 189-190.