Exodus 23:10

The institution of the sabbatical year was designed, To shew what a plentiful land that was, into which God was bringing them, that so numerous a people could have rich maintenance out of the products of so small a country, without foreign trade, and yet could spare the increase of every seventh year. To teach them a confidence in the Divine Providence, while they did their duty, That as the sixth day's manna served for two days meat, so the sixth year's increase should serve for two years subsistence.