To enable the development of industry in an economy requires of the farmer to produce surplus food.
That surplus allows the economy to move beyond subsistence into higher forms of productivity. The shnat sheviit forces the economy to produce surplus food and thus to organize itself so that the production of surplus is a basic standard in the economy.
The sabbatical year both enables the going beyond subsistence as well as the remaining within the band of sova so that the society does not descend into the excesses of excess.
The sabbatical year promotes the institutions of both surplus and sova.