Catechism of the Council of Trent: No Misuse of God's Name
Unjust Oaths
This Commandment is also violated, if justice, which is one of the three conditions of an oath, be wanting. Hence he who swears to commit a mortal sin, for example, to perpetrate murder, violates this Commandment, even though he speak seriously and from his heart, and his oath possess what we before pointed out as the first condition of every oath, that is, truth.
To these are to be added oaths sworn through a sort of contempt, such as an oath not to observe the Evangelical counsels, such as celibacy and poverty. None, it is true, are obliged to embrace these divine counsels, but by swearing not to observe them, one contemns and despises them.
Rash Oaths
This Commandment is also sinned against, and judgment is violated when one swears to what is true and what he believes to be true if his motives are light conjectures and far-fetched reasons. For, notwithstanding its truth, such an oath is not unmixed with a sort of falsehood, seeing that he who swears with such indifference exposes himself to extreme danger of perjury.
Oaths By False Gods
To swear by false gods is likewise to swear falsely. What more opposed to truth than to appeal to lying and false deities as to the true God?
Irreverent Speech
Scripture when it prohibits perjury, says: Thou shalt not profane the name of thy God, thereby forbidding all irreverence towards all other things to which, in accordance with this Commandment, reverence is due. Of this nature is the Word of God, the majesty of which has been revered not only by the pious, but also sometimes by the impious, as is narrated in Judges of Eglon, King of the Moabites.
But he who, to support heresy and the teaching of the wicked, distorts the Sacred Scriptures from their genuine and true meaning, is guilty of the greatest injury to the Word of God; and against this crime we are warned by these words of the Prince of the Apostles: There are certain things hard to be understood, which the unlearned and unstable wrest, as they do also the other Scriptures, to their own destruction.
It is also a foul and shameful contamination of the Scripture, that wicked men pervert the words and sentences which it contains, and which should be honoured with all reverence, turning them to profane purposes, such as scurrility, fable, vanity, flattery, detraction, divination, satire and the like—crimes which the Council of Trent commands to be severely punished.
Neglect Of Prayer
In the next place, as they honour God who, in their affliction implore His help, so they, who do not invoke His aid, deny Him due honour; and these David rebukes when he says: They have not called upon the Lord, they trembled for fear where there was no fear.
Blasphemy
Still more enormous is the guilt of those who, with impure and defiled lips, dare to curse or blaspheme the holy name of God—that name which is to be blessed and praised above measure by all creatures, or even the names of the Saints who reign with Him in glory. So atrocious and horrible is this crime that the Sacred Scriptures, sometimes when speaking of blasphemy use the word blessing.
Sanction of this Commandment
As, however, the dread of punishment has often a powerful effect in checking the tendency to sin, the pastor, in order the more effectively to move the minds of men and the more easily to induce to an observance of this Commandment, should diligently explain the remaining words, which are, as it were, its appendix: For the Lord will not hold him guiltless that shall take the name of the Lord his God in vain.
In the first place (the pastor) should teach that with very good reason has God joined threats to this Commandment. From this is understood both the grievousness of sin and the goodness of God toward us, since far from rejoicing in man's destruction, He deters us by these salutary threats from incurring His anger, doubtless in order that we may experience His kindness rather than His wrath. The pastor should urge and insist on this consideration with greatest earnestness, in order that the faithful may be made sensible of the grievousness of the crime, may detest it still more, and may employ increased care and caution to avoid its commission.
He should also observe how prone men are to this sin, since it was not sufficient to give the command, but also necessary to accompany it with threats. The advantages to be derived from this thought are indeed incredible; for as nothing is more injurious than a listless security, so the knowledge of our own weakness is most profitable.
He should next show that God has appointed no particular punishment. The threat is general; it declares that whoever is guilty of this crime shall not escape unpunished. The various chastisements, therefore, with which we are every day visited, should warn us against this sin. It is easy to conjecture that men are afflicted with heavy calamities because they violate this Commandment; and if these things are called to their attention, it is likely that they will be more careful for the future.
Deterred, therefore, by a holy dread, the faithful should use every exertion to avoid this sin. If for every idle word that men shall speak, they shall render an account on the day of judgment, what shall we say of those heinous crimes which involve great contempt of the divine name?‸