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.

By the life of Pharaoh - חי פרעה chey Pharaoh, Pharaoh liveth. As if he had said, As surely as the king of Egypt lives, so surely shall ye not go hence unless your brother come hither. Here therefore is no oath; it is just what they themselves make it in their report to their father, Genesis 43:3 : the man did solemnly protest unto us; and our translators should not have put it in the form of an oath, especially as the original not only will bear another version, but is absolutely repugnant to this in our sense of the word.

Hereby ye shall be proved: (d) By the life of Pharaoh ye shall not go forth hence, except your youngest brother come hither.
(d) The Egyptians who were idolaters, used to swear by their king's life: but God forbids swearing by anyone but him: yet Joseph dwelling among the wicked was corrupted by them.

Hereby ye shall be proved,.... Whether spies, or not, namely, by producing their youngest brother, said to be at home with his father:
by the life of Pharaoh ye shall not go forth hence, except your youngest brother come hither: the phrase, "by the life of Pharaoh", seems to be the form of an oath, as it was common with many nations, especially with the Scythians, who used to swear by the royal throne (a), and the Romans, in later times, by the life, health, and genius of their emperor; and this custom of swearing by the life of their king, or by his head, continued with the Egyptians, as Aben Ezra says, unto his times; though some take this to be a wish or prayer for the life of Pharaoh, and render it, "may Pharaoh live" (b), or, at most, but a strong asseveration, that as dear as the life of Pharaoh was to him, so surely they should not stir from the place where they were, unless their youngest brother Benjamin was brought thither.
(a) Herodot. Melpomene, sive, l. 4. c. 68. (b) "vivat Parhoh", Montanus, Junius & Tremellius; so Ainsworth and Lightfoot.

By the life of Pharaoh--It is a very common practice in Western Asia to swear by the life of the king. Joseph spoke in the style of an Egyptian and perhaps did not think there was any evil in it. But we are taught to regard all such expressions in the light of an oath (Matthew 5:34; James 5:12).