Deuteronomy 8:2-3

And thou shalt remember all the way which Jehovah thy God hath led thee these forty years in the wilderness, that he might humble thee, to prove thee, to know what was in thy heart, whether thou wouldest keep his commandments, or not. And he humbled thee, and suffered thee to hunger, and fed thee with manna, which thou knewest not, neither did thy fathers know; that he might make thee know that man doth not live by bread only, but by everything that proceedeth out of the mouth of Jehovah doth man live.