(Is the Third Commandment concerned only with oaths, or also with the abusive use of the divine name and of speech in general?)
The Third Commandment reaches beyond false and needless oaths to every abusive use of the name of God, and, through it, to the abuse of speech itself. To understand why the commandment stands so high in the Decalogue, the faithful should consider what speech is. God created the universe by speaking, “God said, ‘Let there be light,’ and there was light” (Gen 1:3); “by the word of the LORD the heavens were made” (Psa 33:6), and his eternal Son is himself the Word (Joh 1:1–3). When God made man in his image, he entrusted to him, alone among the animals, two shares in his own creative power: the power of procreation, by which man brings forth new persons bearing the divine image (Gen 1:27–28; 5:3), and the power of speech, by which man, like his Maker, names, blesses, promises, teaches, and builds up, Adam’s first recorded act being the God-like work of naming the creatures (Gen 2:19–20). These two endowments are the most god-like things in us; and for that very reason, they are the two whose abuse is most destructive, as the surrounding commandments confirm, for the Decalogue guards procreation by the Seventh Commandment and speech by the Third and the Ninth. What is holy enough to create is powerful enough to destroy: “death and life are in the power of the tongue” (Prv 18:21).
Therefore, to seize the all-holy Name, the Name by which we are saved (Act 4:12), the Name hallowed in the first petition (see S009) of the Lord’s Prayer, and fling it as a curse, an expletive, or a decoration of anger, is not a trivial habit but a small blasphemy: it takes the most sacred word given to human lips and uses it as a weapon or as refuse. The same judgment falls, in its measure, on all abusive speech, cursing, vile language, malicious mockery, for every human being against whom the tongue is turned bears the image of the God whose name we profess to honor. This is precisely the Apostle James’s argument: “the tongue is a little member, but it boasts great things! See how a small fire can spread to a large forest! The tongue is also a fire! Among all our members, the tongue is a world of wrongdoing which defiles the whole body” (Jas 3:5–6); “no human being can tame the tongue: it is a restless evil, full of deadly poison. With it we bless our God and Father, and with it we curse those who are made in the image of God. Out of the same mouth comes blessing and cursing. My brothers, these things ought not to be so!” (Jas 3:8–10). One organ cannot serve two liturgies: the mouth that receives the holy Mysteries and sings the Trisagion cannot, without contradiction, pour out profanity and cursing, as no spring, says the Apostle, yields both fresh water and bitter (Jas 3:11–12).
Let the Christian therefore treat speech as what it is: a sacred power, exercised before God, for which account will be given, “every idle word that people speak, they will give an account of it in the day of judgment; for by your words you will be justified, and by your words you will be condemned” (Mat 12:36–37). The discipline is positive as well as negative: not only to renounce profanity, cursing, and the vain use of the Name, but to consecrate the tongue to its created purpose, blessing, thanksgiving, truthful and gracious speech that gives grace to those who hear (Eph 4:29; Col 4:6), and above all the calling upon the Name in prayer, for the Name abused by the world is the very Name by which the Christian is saved: “everyone who calls on the Name of the Lord will be saved” (Rom 10:13; see the Study: The Battle of Prayer).
