|Art: Pat Harrison|
One of the reasons for the Sabbatical year is to allow the land to rest for a year, to enhance its fertility [Guide for the Perplexed 3:3] From this it follows that after six consecutive years of intensive agriculture, the land is at its least fertile point in the seven year cycle. So the Torah's promise that the land ''will yield produce (sufficient) for three years'' in the naturally infertile sixth year, is totally irrational, and requires a person to accept an authority which is higher than his mortal understanding.
The Talmud [Sanhedrin 97a] compares the six agricultural years to the six millenia of this world, and the Sabbatical year to the seventh millenium [when the Geula will have arrived].
Since the Jewish people suffer from a gradual regression in spiritual stature as the generations pass, a person might ask ''How could the efforts of the spiritually weak and ''infertile'' sixth millenium bring the true and complete redemption?''
The Torah answers: It is the super-rational self-sacrifice and commitment to Judaism of the final generations of exile that will bring the blessings of the Redemption.
Source: Lubavitcher Rebbe Likutei Sichos vol 27 pp 189-190