Calvin's Commentaries, Vol. 4: Harmony of the Law, Part II, tr. by John King, [1847-50], at sacred-texts.com
12. And ye shall not swear by my name falsely, neither shalt thou profane the name of thy God: I am the LORD.
12. Non jurabitis per nomen meum mendaciter, nec profanabis nomen Dei tui: ego Jehova.
13. ... shalt swear by his name.
13. Per nomen ejus jurabis.
20. ... swear by his name.
20. In nomine ejus jurabis.
Leviticus 19:12. And ye shall not swear by my name falsely. Although Moses is treating of the duties of the Second Table, and had previously forbidden men to deal fraudulently with their neighbors, he still adds this sentence by way of confirmation. It may, however, be inferred from the second clause of the verse that He directly had regard to the glory of God when he says, “Thou shalt not profane the name of thy God.” For raging greediness after gain causes the avaricious and rapacious man not only to defraud men, but to become insolent to God Himself. Moses, therefore, although he is professedly condemning the falsehood and deceit whereby our neighbors are injured, at the same time takes occasion to introduce the declaration that we must beware lest, whilst covetousness impels us to do wrong, injury should be done not only to men but to God Himself also. The word used here, however, is not שוא, shau, as before, but שקר, sheker, which properly signifies deceitfulness; and therefore I have said that it enjoins us to beware lest any one by his perjury should do any injury to his neighbor; nevertheless, that this prohibition has direct reference to the Third Commandment, since Moses especially insists on this point, that God’s name is profaned by perjury, and thus he not only inculcates integrity, but also has regard to religion, that God’s majesty may not be violated. The expression is worthy of notice, “Thou shalt not pollute the name of God,” because God, who is eternal and immutable truth, cannot be more grossly insulted than by being summoned as a witness to falsehood, which is assuredly a shameful and wicked pollution. This was not regarded by the heathen, who, although they pretended to reverence God’s name in their oaths, yet made no scruple of deceiving, if he whom they had promised deserved it. Thyestes in the poet says, “I never have pledged my faith, nor do I pledge it to any faithless person;” 310 since his brother was a villain, he considered that he lay under no valid obligation to him. This is as if God’s majesty were dependent upon men’s deservings, so that it was allowable to call Him to witness whilst we deal deceitfully. Let this, then, be our firm conclusion, that in our oaths God is first to be regarded, whose holy name is more precious than a hundred worlds.
Cic. de Off. 3 28, 29. “Deinde illud etiam apud Actium Fregisti fidem. Neque dedi neque do infideli cuiquam, quanquam ab impio rege dicitur, luculente tamen dicitur. “Nam illud quidem, Neque dedi, neque do fidem in fideli cuiquam,idcirco recte a poeta; quia, cum tractaretur Atreus, personae serviendum fuit.”