Chapter I — What God commands, or forbids, by this second precept of the Decalogue, is explained

I. St. Thomas explains the threefold sense in which the name of God can be used, in these words (II-II, q. 89, in the proem of that same question): "We must now treat of the taking of the divine name. Now the divine name is taken by man in three ways. In one way, by manner of oath, for the confirmation of one's own words; in another way, by manner of adjuration, to induce another; in a third way, by manner of invocation, to pray, or to praise. Of these three we too, following the Angelic Doctor's words, shall have our discourse." For the rest, St. Thomas explains more broadly the several modes by which the name of God can be used in vain. But because our discourse will also be of the various formulas of oaths, we make progress toward explaining these too.

II. Wherefore, since God forbids his name to be usurped in vain, he at the same time commands that this same holy name be honored by us, and that, through it, we swear justly, holily, and with the highest reverence. This precept of the Decalogue, then, contains two things. First, it forbids anyone to despise, pollute, or use the most sacred name of God vainly, or without necessity; and it forbids that anyone swear by it falsely, or rashly, or recklessly. Second, it commands us to praise, venerate, and honor that same holy name with the utmost obedience. This the Catechism of the Council of Trent, on the second commandment, teaches perspicuously (ch. 10): "What this commands, again, and what it forbids, are these: that the name of God is to be honored, and by it holily to be sworn — but that no one is to despise or use the divine name in vain, nor swear by it falsely, or rashly, or recklessly."

III. The divine name, to which we are commanded to show honor and worship, is not taken merely according to the syllables and letters, or the sound of the voice, but as to what the name itself signifies. Now the name to be sworn by, chiefly according to this, betrays the divine majesty and its infinite attributes... . Whatever name, then, expresses the immense majesty of God, we are bound to render honor to those names. For frequently, in the divine Scriptures, God is called Lord, Omnipotent, Most High, Highest, King of Kings, Just, Father of mercies, and by other names, under all of which he is to be honored by us. Wherefore the Catechism of Trent rightly reproves, in the place cited, the superstition of the Jews, in these words: "From this it is easily gathered how empty is the superstition of certain Jews, who dared not pronounce the name of God, as though they were writing it, as if there were some power in those four letters, and not in the divine reality itself."

IV. We praise and honor God, then, when we confess him in the sight of all; when we proclaim his goodness, justice, wisdom, and mercy; when we acknowledge him as the author and maker of all things; when we learn his law and commandments, and strive to carry them out. We honor the divine name when, whether in prosperous or adverse events, we render thanks to God... , as Micah says: "Blessed be the name of the Lord"; or, with David (Psalm 33): "I will bless the Lord at all times: his praise shall be always in my mouth." We further honor the divine name when we implore his aid, that he may free us from evil, preserve us from temptations, and render us strong and steadfast in bearing all calamities, and persevering in the way of virtue. Finally, we worship the name of God when we call God himself as witness, necessity requiring it, to confirm the truth to unbelievers, according to that saying (Deuteronomy 6): "Thou shalt fear the Lord thy God, and shalt serve him only, and thou shalt swear by his name." If you wish more on this subject, consult Natalis Alexander (Bk. IV, ch. 4), where he explains more fully what the Catechism of Trent teaches, in the place cited, §3.