“You shall not invoke the name of the LORD, your God, in vain. For the LORD will not leave unpunished anyone who invokes his name in vain” (Exodus 20:7).
The first thing that the second commandment brings to mind is using God’s name inappropriately or in an otherwise disrespectful manner, like coupling “God” with an expletive. Evangelical theologian John Piper sees it this way and goes further by focusing on the word “vain”, suggesting that the Hebrew word refers to an “emptying”:
“So it doesn’t just refer to a certain tone of voice or a certain use of the word. It’s dealing with God and speaking of God in a way that empties him of his significance.” (link)
This interpretation, however, is too superficial and fails to take into account both the literary and historical context of the biblical text.
In the Ancient Near East invoking the name of a deity in testimony was at the heart of its juridical system. It was how intent was disproven. Note the following laws from the Code of Hammurabi (ca. 1790 BC):
“If a merchant entrust money to an agent (broker) for some investment, and the broker suffer a loss in the place to which he goes, he shall make good the capital to the merchant. If, while on the journey, an enemy take away from him anything that he had, the broker shall swear by God and be free of obligation” (101-102).
“If any one hire an ox, and God strike it that it die, the man who hired it shall swear by God and be considered guiltless” (249).
Penalties for various crimes could be extremely severe and often involved physical mutilation or death. Swearing on the name of God that you are innocent, or didn’t know the specific act was a crime, or that you didn’t intend for it to happen, could get you out of trouble. Consider this law, also from Hammurabi:
“If any one who has not lost his goods state that they have been lost, and make false claims: if he claim his goods and amount of injury before God, even though he has not lost them, he shall be fully compensated for all his loss claimed” (126).
It was believed that god would repay the individual for having falsely sworn in his name. It probably would have been the god Marduk, but Mesopotamians believed in many gods. Taking your chances with Marduk was better than losing a hand or two. I believe the second commandment was a warning to the Hebrews not to take their chances with their God.
The Ancient Egyptians were smart and may have done it differently. The eminent Egyptologist Klaus Baer explained to me once that to make a vow or otherwise swear before a god, one would go to a temple and stand before a statue of a god. The statue, however, might have had a pulley system that was secretly controlled by the temple priest. If the statue moved forward, the vow was accepted; if it moved backward, it was not.
The Catechism, while interpreting the commandment in very broad terms, points to the words of Jesus to explain what it means to Christians today, which is quite different. It has to do with the inherent contradiction of invoking His name on a discretionary basis:
In the Sermon on the Mount, Jesus explained the second commandment: “You have heard that it was said to the men of old, ‘You shall not swear falsely, but shall perform to the Lord what you have sworn.’ But I say to you, Do not swear at all. . . . Let what you say be simply ‘Yes’ or ‘No’; anything more than this comes from the evil one” (Matt. 5:33-34,37). Jesus teaches that every oath involves a reference to God and that God’s presence and his truth must be honored in all speech (ccc: 2153)