Albert Barnes Commentary Leviticus 25:4

"but in the seventh year shall be a sabbath of solemn rest for the land, a sabbath unto Jehovah: thou shalt neither sow thy field, nor prune thy vineyard." — Leviticus 25:4 (ASV)

A sabbath of rest - See the note on Leviticus 23:3. The express prohibition of sowing and reaping, and of pruning and gathering, affords a presumption in favor of the sabbatical year beginning, like the year of Jubilee (Leviticus 25:9), in the first month of the civil year (Leviticus 23:24), the seventh of the sacred year, when the land was cleared of the crops of the preceding year.

The great material advantage of the institution must have been the increased fertility of the soil from its lying fallow one year out of seven, at a time when neither the rotation of crops nor the art of manuring were understood. It must also have kept up a salutary habit of economy in the storing of grain. Compare Genesis 41:48-56. Its great spiritual lesson was that there was no such thing as absolute ownership in the land vested in any person, that the soil was the property of Yahweh, that it was to be held in trust for Him, and not to be abused by overworking, but to be made the most of for the good of every creature which dwelt upon it.