3. Let not thy left hand know By this expression he means, that we ought to be satisfied with having God for our only witness, and to be so earnestly desirous to obey him, that we shall not be carried away by any vanity. It frequently happens, that men sacrifice to themselves rather than to God. Christ therefore wishes, that we should not be distracted by indirect thoughts, but go straight to this object, that we may serve God with a pure conscience.