“Do you swear to tell the truth, the whole truth, and nothing but the truth, so help you God?” Is the third commandment a prohibition against such an oath?
The third commandment says, “You shall not misuse the name of the LORD your God, for the LORD will not hold anyone guiltless who misuses his name” (Exodus 20:7). In this case, misusing the name of God means taking it on as support for one’s truthfulness in an oath or promise. It says in effect, “The truthfulness of my promise rests on the truthfulness of God, and I expect His punishment if I violate it.” Breaking such an oath would thus be misusing God’s name (using it in vain, as the King James version says, using it in an empty or meaningless way).
This is why Leviticus 19:12 says, “Do not swear falsely by my name and so profane the name of your God” and Numbers 30 gives the only exceptions to fulfilling of vows. There are other ways of misusing God’s name that this commandment implies (cursing, using God’s name in a flippant or joking manner, living hypocritically, etc.). But the primary focus is on the seriousness of making a promise on the merit of God’s honesty and then breaking it. It is like saying God did not keep His word.
Deuteronomy 6:13 commanded Israel to swear only by the name of the true God, Yahweh. But Jesus prohibits any oaths in Matthew 5:33-37. Apparently it was common to hear someone swear by “heaven” or something else associated with God as a way of avoiding both keeping one’s word and incurring God’s judgment (Matthew 23:16-22). “After all,” they might say, “I didn’t use God’s name.” Jesus says, “Do not swear at all…simply let your ‘Yes’ be ‘Yes,’ and your ‘No,’ ‘No’ (Matthew 5:34,37). James repeats this in James 5:12.
This does not mean that the one who says ‘Yes’ or ‘No’ is not required to keep his or her word. But it avoids making God responsible for its truthfulness. That is a dangerous thing to do. God will not fail to punish those who misuse His name.
So is it wrong to swear in court? Jesus submitted to an oath in court (Matthew 26:62-64) and Paul used oaths with God’s name (2 Corinthians 1:23; Galatians 1:20). Thus Jesus’ prohibition is likely meant to refer to the oaths of daily conversation which are more liable to being broken. Of course, the seriousness of oaths in certain circumstances still comes under the standard of the third commandment.
Are you good for your word? Does your life, as well as your words, reflect the righteous character of God? Do not let your life or your words end up sending a message that God is less than you represent Him to be. He will not hold us guiltless.