Har Sinai is a kind of conduit, a connector between Heaven & Earth. It’s message is that every act we perform, every Mitzva we keep, reverberates & impacts both above & below.
The rationale behind Shmita, is to create for us a “Shabbat Shabbaton” every 7 years. Like the contemporary Sabbatical, this results in a complete change in our routine, a break from the norm, a chance to recharge the batteries & then make a new start, refreshed & reinvigorated.