It is strange that the Torah specifically says that these commands it now gives about Sabbaticals and the Jubilee were given on Sinai. Weren’t all the laws supposed to have been given on Sinai? Rashi quotes the Midrash that says that it simply reiterates the fact that Sinai was the source of everything. But it does seem strange that this comes directly after a case many years after Sinai in which Moses needs to go back to consult with God. Sinai as the origin, but not the end of Divine Law giving?
Also noteworthy is that these laws are predicated in “when you arrive in the Land.” Hinting at the debate over whether all or only some of the laws were intended to apply only in Israel.The seventh Year Shmitah, release, sounds a lot like a variation on medieval crop rotation, giving agricultural land a breather in one way or another from over use. As the Torah says, “It is a rest of rests for the land.”
It seems that the Shmitah was always observed where possible. But for a long time, there was little Jewish agricultural activity in the Land of Israel. That began to change with the nineteenth century pioneers from Eastern Europe who began to drain the swamps of the north. They were struggling to survive. To get around the problem the Chief Rabbinate arranged for the land to be “sold” to a friendly Arab for the duration. Like selling Hametz over Pesah. Increasingly conditions have improved so that more and more people in Israel now keep Shmitah without using the old device off selling the land.
The Seventh Year released bonded Israelites who had debits to pay off by working for their creditor. Or because they could not afford to feed themselves and their children so they sold themselves into servitude. In addition, debts incurred were released. In ancient times lending was only an act of charity or to help someone set up in business. The Torah did not want people to be burdened indefinitely by debt.
This too must have been common because as society began to shift from agricultural to commercial, the problem of lending when the seventh year released all debts meant that lenders withdrew for fear of losing their money. Hillel then created the Prosbul, that transferred the debt to the Beth Din who were not subject to the release. And they ensured the money was returned. It was also a year that by being freed from agricultural work many who wanted to could devote themselves to study. Hence our modern use of the word “sabbatical.”