The Purpose of the Mitzvah of Shemitah

Parshat Behar begins with the commandment of shemitah, the requirement to let the Land of Israel lie fallow once every seven years. The Torah states, (Vayikra 25:2)

דבר אל בני ישראל ואמרת אליהם כי תבואו אל הארץ אשר אני נתן לכם ושבתה הארץ שבה ליקוק

Speak unto the children of Israel, and say unto them: When you come into the land which I give you, then shall the land keep a sabbath unto the LORD.

Rashi, in his commentary to the pasuk writes,

שבת לה' - לשם ה', כשם שנאמר בשבת בראשית

A Sabbath unto the Lord - for the sake of the Lord, just as it says by the Sabbath of Creation

In explaining the words of Rashi, Rabbi Amos Chacham in Daat Mikra explains,

שבת לה’ והכוונה, שבת היא לכבוד ה’, ולאו דווקא לטובת האדם, ולאו דווקא לטובת האדמה.

A Sabbath unto the Lord - and the intent is that the Sabbath be for the Lord's honor, and not necessarily for the benefit of man and not necessarily for the benefit of the Land

.

Accordingly, the Torah tells us that the purpose of observing the shemitah year is a tribute to Hashem and does not serve any other purpose.
However the Rambam, in his Moreh Nevuchim (3:39) argues,

ואמנם כל המצוות אשר סיפרנום בהלכות שמיטה ויובל, מהם לחמלה על בני אדם והרחבה לבני אדם כולם, כמו שאמר "ואכלו אביוני עמך ויתרם תאכל חית השדה" (שמות כ"ג י"א) ושתוסיף הארץ תבואתה ותתחזק בעומדה שמוטה.

Of all the commandments which we have listed pertaining to shemitah and yovel, some show compassion for certain people and broadening the reach of mankind as a whole, as it is written, 'and the poor of your nation shall eat and the leftovers shall be eaten by the animals of the field.' And so that the land should increase its crops and become strengthened from lying fallow.

This opinion of the Rambam is in direct opposition to Rashi's view on shemitah. According to the Rambam the mitzvah is to benefit man in that it provides the poor with food, since crops during the seventh year are hefker, ownerless. In addition it strengthens the land and allows it to produce more crops in subsequent years by letting it rest. Rashi, however disagrees and says that the institution of shemitah has nothing to do with people or land, it is simply a tribute to Hashem conducted once every seven years.