15. By the life of Pharaoh. From this formula of swearing a new question is raised; for that which is commanded in the law, that we should swear only by the name of God, had already been engraven on the hearts of the pious; since nature dictates that this honor is to be given to God alone, that men should defer to his judgment, and should make him the supreme arbiter and vindicator of faith and truth. If we should say that this was not simply an oath, but a kind of obtestation, the holy man will be, in some degree, excusable. He who swears by God wishes him to interpose in order to inflict punishment on perjury. They who swear by their life or by their hand, deposit, as it were, what they deem most valuable, as a pledge of their faithfulness. By this method the majesty of God is not transferred to mortal man; because it is a very different thing to cite him as witness who has the right of taking vengeance, and to assert by something most dear to us, that what we say is true. So Moses, when he calls heaven and earth to witness, does not ascribe deity to them, and thus fabricate a new idol; but, in order that higher authority may be given to the law, he declares that there is no part of the world which will not cry out before the tribunal of God, against the ingratitude of the people, if they reject the doctrine of salvation. Notwithstanding, there is, I confess, in this form of swearing which Joseph uses, something deserving of censure; for it was a profane adulation, among the Egyptians, to swear by the life of the king. Just as the Romans swore by the genius of their prince, after they had been reduced to such bondage that they made their Caesar equal to gods. Certainly this mode of swearing is abhorrent to true piety. Whence it may be perceived that nothing is more difficult to the holy servants of God than to keep themselves so pure, while conversant with the filth of the world, as to contract no spots of defilement from it. Joseph, indeed, was never so infected with the corruptions of the court, but that he remained a pure worshipped of God: nevertheless we see, that in accommodating himself to this depraved custom of speaking, he had received some stain. His repetition of the expression shows, that when any one has once become accustomed to evil, he becomes exceedingly prone to sin again and again. We observe, that they who have once rashly assumed the license of swearing, pour forth an oath every third word, even when speaking of the most frivolous things. So much the greater caution ought we to use, lest any such indulgence should harden us in this wicked custom.