The following is excerpted from the Westminster Longer Catechism, as available in an e-Sword module:
Question 111: Which is the third commandment?
Answer: The third commandment is, Thou shalt not take the name of the Lord thy God in vain: for the Lord will not hold him guiltless that takes his name in vain.
Question 112: What is required in the third commandment?
Answer: The third commandment requires, That the name of God, his titles, attributes, ordinances, the Word, sacraments, prayer, oaths, vows, lots, his works, and: Whatsoever else there is whereby he makes himself known, be holily and reverently used in thought, meditation, word, and writing; by an holy profession, and answerable conversation, to the glory of God, and the good of ourselves, and others.
Question 113: What are the sins forbidden in the third commandment?
Answer: The sins forbidden in the third commandment are, the not using of God’s name as is required; and the abuse of it in an ignorant, vain, irreverent, profane, superstitious, or wicked mentioning, or otherwise using his titles, attributes, ordinances, or works, by blasphemy, perjury; all sinful cursings, oaths, vows, and lots; violating of our oaths and vows, if lawful; and fulfilling them, if of things unlawful; murmuring and quarreling at, curious prying into, and misapplying of God’s decrees and providences; misinterpreting, misapplying, or any way perverting the Word, or any part of it, to profane jests, curious or unprofitable questions, vain janglings, or the maintaining of false doctrines; abusing it, the creatures, or anything contained under the name of God, to charms, or sinful lusts and practices; the maligning, scorning, reviling, or anywise opposing of God’s truth, grace, and ways; making profession of religion in hypocrisy, or for sinister ends; being ashamed of it, or a shame to it, by unconformable, unwise, unfruitful, and offensive walking, or backsliding from it.
Question 114: What reasons are annexed to the third commandment?
Answer: The reasons annexed to the third commandment, in these words, “The Lord thy God,” and, “For the Lord will not hold him guiltless that takes his name in vain,” are, because he is the Lord and our God, therefore his name is not to be profaned, or any way abused by us; especially because he will be so far from acquitting and sparing the transgressors of this commandment, as that he will not suffer them to escape his righteous judgment, albeit many such escape the censures and punishments of men.
I was asked the question of what I thought taking the Lord’s name in vain meant. Typically I tread on the side of the ancient Jews — that taking His name in vain actually required usage of His name (Yahweh). Erring on the side of caution, they removed God’s name from the Scriptures so that it’d be that much harder to commit the sin of taking it in vain.
However, those who put together the Westminster Catechism were no fools, and it has proven to be a time-tested outline of sorts of orthodox belief.
And they explain that third commandment quite a bit better than I could.
In light of their answer to which sins it forbids, it really is far less surprising to read the Book of James and see so much admonition for us to just keep our mouths shut.
But if I might add, when we claim to be Christians, we are in essence taking the Lord’s name — we are claiming to be part of the Bride of Jesus, even applying His “surname” to ourselves. As Christians, are we living up to His name? Obviously, there will be sins — we are, after all — human. Are we doing all we can to be holy as Christ is holy, though? Or are we taking His name in vain?