Thou shalt not take the name of the Lord thy God in vain. Found in Exodus 19 as one of the Ten Commandments delivered by Moses to the Israelites at the foot of Mount Sinai in the Sinai Peninsula of South Egypt. We generally take this to mean simply using God’s name in the context of a “dirty” or “filth” expression, and indeed, it is most often used in that context.
But in some cases, like the Jews during the Second Temple period of 515 BC and 70, took this to mean invoking the name God in any context. So they refrained at all costs.
So what exactly does “vain” mean?
If we retreat back to the original text of the Hebrew bible, the word שוא can have a variety of meanings and synonyms, such as vanity, emptiness of speech, even lying. So we might conclude that the commandment simply refers to misusing the lord’s name in any capacity. While this would certainly apply to the faithful without questions, to those who believe in the lord, it’s actually quite tricky to apply this logic to a non-believer. After all, to misuse requires the acknowledgment that he exists, and that the commandment should be adhered to – of which neither condition would apply to an atheist. But we’ll focus on believers for now, and leave that particular point aside.
Misuse in the above sense could amount to a whole host of definitions. Like Isaiah scolded the Israelites, using the name of God while also worshiping other gods was hypocrisy, and therefore a sin. And in Jeremiah 34:16 we find But ye turned and polluted my name, and caused every man his servant, and every man his handmaid, whom ye had set at liberty at their pleasure, to return, and brought them into subjection, to be unto you for servants and for handmaids.
And in the Sermon on the Mount, recorded in the Gospel of Matthew, Jesus tells his followers, But I say unto you, Swear not at all; neither by heaven; for it is God’s throne. Reinforced in James, the idea here is that one’s word should be enough to uphold the truth, and should never require invoking the name of God.