Because they could not have borne it if when giving the law for the sabbath God had said, “Do your good works on the sabbath, but do not the works that are evil,” therefore he restrained them from all alike. “You must do nothing at all,” he says, and even so they were not kept in line. But in the very act of giving the law of the sabbath he signified, though in shaded language, that he restricts them from evil works only, for he says, “You must do no work, except what shall be done for your life.” And in the temple too all went on each sabbath with even more diligence and double toil. Thus even by shadows he was secretly opening them to the truth.
[AD 407] John Chrysostom on Numbers 28:9-10