Parshas Behar begins with the mitzvah of shemitta. "When you enter the land that I give you, the land should rest a Shabbos for Hashem" (Vayikra 25, 2). Rashi explains that "for Hashem" means for the sake of Hashem. He continues that we find this exact wording in the Aseres Hadibros (Shemos 20, 10) with regard to the Shabbos observed every week, "And the seventh day shall be a Shabbos for Hashem." What lies behind Rashi's reference? What connection is there between Shabbos and Shemitta?
Rav Wolbe (Shiurei Chumash) cites a Ra'avad to aid us in understanding the above connection. The Ra'avad, in his introduction to Ba'alei Hanefesh, maintains that numerous mitzvos share a common denominator. Hashem commanded us to perform these mitzvos to demonstrate that it is He Who is in charge of creation and not us. Both Shemitta and Shabbos fall under this category of mitzvos. During Shemitta we desist entirely from working the land and all the produce that grows during this year is free for the taking. It is not our land, rather it belongs to Hashem.
Likewise, on Shabbos we are commanded to refrain from performing the 39 melachos. These melachos are all similar in that they are all, in some way, actions which create. Therefore, on Shabbos we must refrain from all such actions to demonstrate that we are ceasing to create for He is the sole Creator and Landlord of the world.
Shemitta is an infrequent and uncommon mitzvah being that it only occurs once every seven years and it applies only in Eretz Yisrael. On the other hand, Shabbos occurs weekly and it is relevant in every country in the world. It isn't just a day off from work and an opportunity to spend time with family and friends. It is an important lesson in the proper perspective of life. Hashem runs the world and we are simply caretakers. It isn't our world into which Hashem has to gain entrance. Rather, it is Hashem's world that we have the zechus of entering, and consequently we must faithfully follow His precepts.