nce every seven years, we observe a year of shemitah, during which we refrain from working the land and growing new produce. For our sustenance in the shemitah year, G-d promises that in the sixth year the earth will yield much more produce than it normally does, providing enough food to last for two and a half years, until the new crops grow in the year after shemitah.
The tremendous output that G-d promises for the sixth year utterly defies the earth's natural ability. For the sixth year's crop would naturally be smaller and weaker than that of the previous years, as the nutrients in the soil deplete somewhat after five consecutive years of planting. In fact, this is one of the reasons suggested for the observance of Shemitah in the seventh year, to ensure that the nutrients in the earth will have a chance to replenish (see Moreh Nevuchim, 3:39). Nevertheless, G-d promises that specifically the produce of the sixth year will be greater than the crop of any other year.
This promise is likewise reflected in our efforts to bring about the coming of Moshiach and the long-awaited Redemption. The Talmud (Sanhedrin 97a) compares the whole of human history to the seven-year shemitah cycle. After six thousand years of human effort to develop G-d's world, the seventh millennium will be a sabbatical era, holy and sanctified to G-d, namely, the era of Moshiach.
Like in the sixth year of the shemitah cycle, the question of "what will we eat in the seventh year?" is strongest in the sixth millennium. For with every passing generation, we have only become weaker in our sensitivity to holiness than the generations that preceded us. How can it be that our impoverished deeds today will succeed at bringing about the coming of Moshiach if theirs did not?
To this G-d responds with the guarantee, "I will command my blessing to you in the sixth year;" it is precisely your simple devotion and loyalty despite the weariness of thousands of years of exile that will elicit the extraordinary blessings of the era of Moshiach.
—Likkutei Sichos, vol. 27, pp. 189-190