You shall not oppress a stranger, for you know the feelings of the stranger, having yourselves been strangers in the land of Egypt. Six years you shall sow your land and gather in its yield; but in the seventh you shall let it rest and leave it [let it lie fallow]. Let the needy among your people eat of it, and what they leave let the wild beasts eat. You shall do the same with your vineyards and your olive groves.

Moses Maimonides 12th century

(24) It is a positive commandment to annul [ownership of] everything that comes out of the ground in the seventh year as [the Torah] says in the seventh you shall let it rest and leave it. (Exodus 23:11) ... Everything should be declared ownerless and everyone has equal claim as as it says (ibid.) and the poor of your people will eat it.

Midrash, 2nd century CE

And in seventh you shall let it rest and lie fallow (Exodus 23:11) [This is written so that one does not think: "Didn't the Torah institute this so that the poor shall eat it? I shall gather it in and distribute it to the poor!"

It is, therefore, written And the seventh year it shall lie fallow and leave it. This teaches that one must allow breaches in the fence. However, the sages allowed repairs to be made [in the fences] for Tikkun Ha-Olam (social good).

from the Mishnah, 200 BCE-200 CE

There are four human outlooks. One who says "What is mine is mine, and what is yours is yours." This is a middling outlook. Some say this is the outlook of Sodom.

"What is mine is yours, and what is yours is mine" is an am ha'arets (uneducated person).

"What is mine is yours, and what is yours is yours" is a pious person.

"What is yours is mine, and what is mine is mine" is a wicked person.

16th century

The year of Shmitah…promotes a sense of fellowship and peace...for one is not allowed to exercise over any of the seventh year produce the right of private ownership. And this inevitably promotes peace since hostility originates from the "what's mine is mine," outlook.... [In the seventh year] all are equal, and this is the real essence of peace.

19th century

....Shmitah corresponds to the outlook of “what is mine is yours” [Pirkei Avot]. Though The land was given to humankind (Psalms 115:16) so that one may acquire the land and bring good things from it.... Nonetheless in the seventh year one gives the land to the Holy Blessed One. At this time one ceases from labor one one's own property in accordance with God's will and keeps God's ordinances. This is called “what is mine is yours,” meaning, one grants to God all of one's property that comes from the earth.

5th century

[The Psalms refer to] The mighty in strength that fulfill God's word. (Psalms 103:20). Of whom does this verse speak? Rabbi Isaac said, “The verse speaks of those who observe the Sabbatical Year. It is not uncommon for a person to do a mitzvah one day, or for a single Shabbat, or for a month - but for the entire year? But one who sees one's land surrounded [by people coming to take from it], and one's vines surrounded, and still must pay taxes and yet remains silent - is there anyone mightier than this?"