49] “You are not to take the name of God in vain.”
 Just as the First Commandment instructs the heart and teaches faith, so this commandment leads us outward and directs the lips and tongue into a right relationship with God. For the first things that burst forth and emerge from the heart are words. As I have taught above how to answer the question of what it means to have a god, so you must learn to understand simply the meaning of this and all the other commandments and apply it to yourself.
 If you are asked, “What does the Second Commandment mean?” or, “What does it mean to take the name of God in vain or to misuse it?” you should answer briefly: “It is a misuse of God’s name if we call upon the LORD God in any way whatsoever to support falsehood or wrong of any kind.” What this commandment forbids,  therefore, is appealing to  God’s name falsely or taking his name upon our lips when our heart knows or should know that the facts are otherwise—for example, when taking oaths in court and one party lies about the other. God’s name cannot be abused more flagrantly than when it is used to lie and deceive. Let this be the simplest and clearest explanation of this commandment.
From this all people can figure out for themselves when and in how many ways God’s name is abused, although it is impossible to enumerate all its misuses. To discuss it briefly, however, misuse of the divine name occurs first of all in business affairs and in matters involving money, property, and honor,  whether publicly in court or in the marketplace or wherever someone commits perjury and swears a false oath in God’s name or by his own soul. This is especially common in marriage matters when two people secretly betroth themselves to each other and afterward deny it with an oath.  The greatest abuse, however, is in spiritual matters, which affect the conscience, when false preachers arise and present their lying nonsense as God’s Word.
See, all of this is an attempt to deck yourself out with God’s name or to put up a good front and justify yourself with his name, whether in ordinary worldly affairs or in sophisticated and difficult matters of faith and doctrine. Also to be numbered among the liars are the blasphemers, not only the very crass ones who are known to everyone and disgrace God’s name flagrantly—they should take lessons from the hangman, not from us— but also those who publicly slander the truth and God’s Word and consign it to the devil. There is no need to say anything more about this now.
Let us learn and take to heart how much is at stake in this commandment and diligently guard against and avoid every misuse of the holy name as the greatest sin that can be committed outwardly. Lying and deceiving are themselves great sins,  but they become much more serious when we try to justify and confirm them by invoking God’s name and thus make it into a cloak to hide our shame. Thus one lie becomes two—indeed, a whole pack of lies.
Therefore God has added a solemn threat to this commandment: “For the LORD will not acquit anyone who misuses his name.”  This means that no one will be let off or go unpunished. As little as God will permit the heart that turns away from him to go unpunished, just as little will he permit his name to be used to disguise a lie.  Unfortunately it is now a common affliction throughout the world that there are just as few who do not use God’s name for lies and all kinds of wickedness as there are few who trust in God with their whole heart.
By nature we all have this lovely virtue that whenever we commit a wrong we like to cover it and gloss over our disgrace so that no one may see or know it. No one is so audacious as to boast of the wickedness he or she has committed. We prefer to act in secret without anyone knowing about it. When someone is caught, then God and his name must be dragged into it, so that the dirty business may be made honorable and the disgrace noble.  That is the common way things go in the world, and, like a great flood, it has inundated all lands. Therefore we get what we deserve: plague, war, famine, fire, flood, wayward spouses and children and servants, and troubles of every kind. Where else could so much misery come from? It is a great mercy that the earth keeps on supporting and feeding us.
 Above all else, therefore, our young people should be strictly required and trained to hold this as well as the other commandments in high regard. Whenever they violate them, we must be after them at once with the rod, confront them with the commandment, and continually impress it upon them, so that they may be brought up not merely with punishment but with reverence and fear of God.
 Now you understand what it means to take God’s name in vain. To repeat it briefly, it is either simply to lie and assert under his name something that is not true, or it is to curse, swear, practice magic, and, in short, to do evil of any sort.
 In addition, you must also know how to use the name of God properly. With the words, “You are not to take the name of God in vain,” God at the same time gives us to understand that we are to use his name properly, for it has been revealed and given to us precisely for our use and benefit.  Therefore, since we are forbidden here to use his holy name in support of falsehood and wickedness, it follows, conversely, that we are commanded to use it in the service of truth and of all that is good—for example, when we swear properly where it is necessary and required, or also when we teach properly, or, again, when we call on God’s name in time of need, or thank and praise him in time of prosperity, etc. All of this is summarized in the command in Psalm 50[:15*]: “Call on me in the day of trouble; I will deliver you, and you shall glorify me.” All of this is what it means to call upon God’s name to support the truth and to use it devoutly. In this way his name is hallowed, as we pray in the Lord’s Prayer.
 Here you have the substance of the entire commandment explained. When it is understood in this way, you have easily solved the question that has troubled many teachers: why swearing is forbidden in the gospel, yet Christ, St. Paul, and other saints often took oaths.  The explanation is briefly this: We are not to swear in support of evil (that is, to a falsehood) or unnecessarily; but in support of the good and for the advantage of our neighbor we are to swear. This is a truly good work by which God is praised, truth and justice are confirmed, falsehood is refuted, people are reconciled, obedience is rendered, and quarrels are settled. For here God himself intervenes and separates right from wrong, good from evil.  If one party swears falsely, there follows judgment: that person will not escape punishment. Although it may take a long time, nothing such people do will succeed in the end; everything gained by the false oath will slip through their fingers and will never be enjoyed.  I have seen this in the case of many who broke their promise of marriage under oath; they never enjoyed a happy hour or a healthful day thereafter, and thus they came to a miserable end with their body, soul, and possessions.
 Therefore I advise and urge, as I have done before, that by means of warning and threat, restraint and punishment, children be trained in due time to beware of lying and especially to avoid calling upon God’s name in support of it. Where they are allowed to act in this way, no good will come of it. It is evident that the world is more wicked than it has ever been. There is no government, no obedience, no fidelity, no faith—only perverse, unbridled people whom no teaching or punishment can help. All of this is God’s wrath and punishment upon such willful contempt of this commandment.
 On the other hand, one must urge and encourage children again and again to honor God’s name and to keep it constantly upon their lips in all circumstances and experiences, for the proper way to honor God’s name is to look to it for all consolation and therefore to call upon it. Thus, as we have heard above, first the heart honors God by faith and then the lips by confession.
 This is also a blessed and useful habit, and very effective against the devil, who is always around us, lying in wait to lure us into sin and shame, calamity and trouble. He hates to hear God’s name and cannot long remain when it is uttered and invoked from the heart.  Many a terrible and shocking calamity would befall us if God did not preserve us through our calling upon his name. I have tried it myself and have indeed experienced that often a sudden, great calamity was averted and vanished in the very moment I called upon God. To defy the devil, I say, we should always keep the holy name upon our lips so that he may not be able to harm us as he would like to do.
 For this purpose it also helps to form the habit of commending ourselves each day to God—our soul and body, spouse, children, servants, and all that we have—for his protection against every conceivable need. This is why the Benedicite, the Gratias, and other evening and morning blessings were also introduced and have continued among us.  From the same source comes the custom learned in childhood of making the sign of the cross when something dreadful or frightening is seen or heard, and saying, “LORD God, save me!” or, “Help, dear Lord Christ!” and the like. Likewise, if someone unexpectedly experiences good fortune—no matter how insignificant—he or she may say, “God be praised and thanked!” “God has bestowed this upon me!” etc.—just as children used to be taught to fast and pray to St. Nicholas and other saints. But these practices would be more pleasing and acceptable to God than life in a monastery or Carthusian holiness.59
 See, with simple and playful methods like this we should bring up young people in the fear and honor of God so that the First and Second Commandments may become familiar and constantly be practiced. Then some good may take root, spring up, and bear fruit, and people may grow to adulthood who may give joy and pleasure to an entire country.  That would also be the right way to bring up children, while they may be trained with kind and agreeable methods. For what a person enforces by means of beatings and blows will come to no good end. At best, the children will remain good only as long as the rod is on their backs.
 But this kind of training takes root in their hearts so that they fear God more than they do rods and clubs. This I say plainly for the sake of the young people, so that it may sink into their minds, for when we preach to children we must talk baby talk. We have prevented the misuse of the divine name and taught its proper use, not only by how we speak but also by the way we act and live, so that everyone may know that God is well pleased with the right use of his name and will just as richly reward it as he will terribly punish its misuse.