from Vayikra 25:1-4
The LORD spoke to Moses on Mount Sinai: Speak to the Israelite people and say to them: When you enter the land that I assign to you, the land shall observe a sabbath of the LORD. Six years you may sow your field and six years you may prune your vineyard and gather in the yield. But in the seventh year the land shall have a sabbath of complete rest, a sabbath of the LORD: you shall not sow your field or prune your vineyard.
Rashi
What has the matter of the Sabbatical year to do with Mount Sinai that Scripture felt compelled to expressly state where it was commanded? Were not all commandments given on Sinai?
Vayikra 25:7
your cattle and the beasts in your land may eat all its yield
Vayikra 25:23
But the land must not be sold beyond reclaim, for the land is Mine; you are but strangers resident with Me.
Sifra, Behar
“for strangers and settlers are you:” Do not make yourselves foremost.
Rabbi Adin Steinsaltz
With the acceptance of the Torah as an inner way of life, as an inner map, [the Jews] encumber themselves with the responsibility and obligation of a priesthood not confined to a particular time or place but for all of life. From this perspective, the whole world is a holy temple, and one that has to be constantly purified and sanctified anew.
As our exploration of the Sanctuary comes to a close we come to the realization that the entire world is a sanctuary.
Rabbi Adin Steinsaltz
An analysis of the laws of Shemitta shows that the matter of “and the wild animals that are in your land” is a very important detail. … [it points to] the fundamental restoration of ownership to God; He is the owner, and we are mere strangers and sojourners in His land. Once every several years, the ownership is removed from our hands … therefore everything that is here belongs to Him. To ensure that we rememb er this, He takes away from us the exclusive right to use things, returning everything to its original residents — the animals, the beasts, and the dogs.
…
What, then does all this have to do with Mount Sinai? Shemitta has to do with Mount Sinai in that this parasha is the essence of what happened at Mount Sinai. … The concept of “a kingdom of Priests” is the essence of our service. As the Ibn Ezra and others explain, “Priests’ in this context means servants: You are God’s servants. … We cannot have true ownership of anything … If we think that we are successful on our own merits and that everything is our own, then God will simply take it back. But if we are unsuccessful and lose everything, He will provide for us.
The descriptions of the care the priests take in performing sacrifices, their need to perfect themselves in the service of God, is a model for us to act in the world.
Vayikra 25:20-21
And should you ask, “What are we to eat in the seventh year, if we may neither sow nor gather in our crops?” I will ordain My blessing for you in the sixth year, so that it shall yield a crop sufficient for three years.
Rabbi Yehudah Leib
… Jews should understand that miracles and nature are all one. In fact there is no miracle so great and wondrous as nature itself, the greatest wonder we can know.