ובשנה השביעת שבת שבתון יהיה לארץ
But in the seventh year the land shall have a sabbath of complete rest… 
The Zohar says that this rest for the land is, like Shabbat, for the people of the land, too:
כמה דשבת נייחא הוא דכלא
שמטה נייחא דכלא
נייחא הוא דרוחא וגופא
(k’ma d’sha’bat nay’cha hu d’cho’la
sh’me’ta nay’cha d’cho’la
nay’cha hu d’ru’cha v’gu’fa)
“As Shabbat is rest for all, Sh’me’ta [the 7th year] is rest for all; rest for spirit and body.” 
Why a “sabbath year” every 7th year? Nachmanides and others, following the Zohar, see in the recurring number “7” an equation between the 7th year and the 7th day of Creation:
“The Ramban [Nachmanides] taught that “the comparison between the shemittah [7th year] and Shabbat is that both bear testimony to G-d’s creation of the universe in 6 days and His rest on the 7th.” 
We “pause” from our work on the 7th day or year, then, to recognize G-d as the Creator — the Source — of all that happens, by looking back on all that has happened in the previous 6 days or years, and ascribing it to G-d. Recognizing G-d as Creator (in itself no small spiritual achievement), as it deepens in us, becomes “contemplation,” as I discussed in an earlier piece.  As it does, it leads us to worship (“honor,” in its older English meaning) G-d.
Ordinarily, we worship by doing. Here, we worship by not doing. Or, we might say, the “doing” of the 7th day or year is the work of “recognizing and remembering” our spiritual Source.
“The [7th] year must be treated as holy like the Sabbath day.” 
Rabbi W. Gunther Plaut, whose Torah-commentary has become standard in Reform Judaism, likewise understands this as an act of worship:
“The sabbatical year may have been of practical benefit in preventing exhaustion of the soil, but that was not the law’s intent. It was rather an expression of the Sabbath idea…” 
He describes the “Sabbath idea” in commenting on the commandment to observe Shabbat:
“…its mood is both serene and joyous…it is the time for recollecting G-d’s goodness and acknowledging G-d’s sovereignty; it provides for social balm, intellectual expansion and a shutting out of the day’s cares. It is spiritually and physically restorative…” 
The sabbatical, then, may be for the sake of the land, but it’s at least as much for the sake of those who work the land — us. In it, we transcend a life of work alone. It allows us to renew our perspective on life as coming from a Divine, Benevolent Source. It gives us a chance to replenish our energy for our life and work; to begin a new cycle with self-less enthusiasm.
Steven Hill (“Mission: Impossible”/TV; “Yentl”; “Law & Order”), a founding member of “The Actor’s Studio” who is also Orthodox-Jewish in personal practice, likewise used a “sh’me’ta” metaphor with regard to working in the arts:
“I don’t think an actor should act every single day. I don’t think it’s good for the so-called creative process. You must have periods when you leave the land fallow, let it revitalize itself.” 
Of course, by “the land,” he means here the artist him/herself.
What is it that “revitalizes” the land, the farmer, or the artist? What “revitalizes” us?
It’s the Source of the 6 days of Creation, that exists no less in us as a Source of Peace, Hope, Energy and Healing.
“The Mind that called everything into existence is G-d, and His dwelling place is in the world He created.” 
It will express itself in us if we let it — if we “worship” it; “honor” it; recognize its presence in and around us and in all that happens to us. 
Worshipping G-d, we become most fully “human,” too.
Pharaoh would forbid us this, in favor of endless toil; endless acquisition and conquest.
Torah guarantees it for us.
It only remains for us to take for ourselves the sabbaticals that we’re offered.