Even as the Lord told Israel they could work six days, but that they had to rest the seventh day, so it was for the land in years,
“Six years you shall sow your land and gather in its produce, but the seventh year you shall let it rest and lie fallow, that the poor of your people may eat; and what they leave, the beasts of the field may eat. In like manner you shall do with your vineyard and your olive grove” (Exodus 23.10, 11).
The Lord did not want them to overwork their bodies, and He did not want them to overwork their land, or anything else.
He wanted His people to work, for He told them to work six days a week, and to work the land for six years, and He knew that six days and six years were the right amount of work, and that the seventh day and the seventh year provided the right break.
This also taught Israel to rely upon the Lord, because He would provide enough in the sixth year to last through the end of the eighth year.
If they kept the land Sabbath, they would do so because they trusted the Lord.