Thus you now understand what. it is to take God's name in vain, that is (to recapitulate briefly), either simply for purposes of falsehood, and to allege God's name for something that is not so, or to curse, swear, conjure, and, in short, to practice whatever wickedness one may. Besides this you must also know how to use the name [of God] aright. For when saying: Thou shalt not take the name of the Lord thy God, in vain, He gives us to understand at the same time that it is to be used properly. For it has been revealed and given to us for the very purpose that it may be of constant use and profit. Hence it is a natural inference, since using the holy name for falsehood or wickedness is here forbidden, that we are, on the other hand, commanded to employ it for truth and for all good, as when one swears truly where there is need and it is demanded. So also when there is right teaching, and when the name is invoked in trouble or praised and thanked in prosperity etc.; all of which is comprehended summarily and commanded in the passage Ps. 50, 15: Call upon Me in the days of trouble; I will deliver thee, and thou shalt glorify Me. For all this is bringing 't into the service of truth, and using it in a blessed way, and thus His name is hallowed, as we pray in the Lord's Prayer. Thus you have the sum of the entire commandment explained. And with this understanding the question with which many teachers have troubled themselves has been easily solved, to wit, why swearing is prohibited in the Gospel, and yet Christ, St. Paul, and other saints often swore. The explanation is briefly this: We are not to swear in support of evil, that is, of falsehood, and where there is no need or use; but for the support of good and the advantage of our neighbor we should swear. For it is a truly good work, by which God is praised, truth and right are established, falsehood is refuted, peace is made among men, obedience is rendered, and quarrels are settled. For in this way God Himself interposes and separates between right and wrong, good and evil. If one part swears falsely, he has his sentence that he shall not escape punishment, ad though it be deferred a long time, he shall not succeed; that all that he may gain thereby will slip out of his hands, and he will never enjoy it; as I have seen in the case of many who perjured themselves in their marriage-vows, that they have never had a happy hour or a healthful day, and thus perished miserably in body, soul, and possessions.