Above all, my brothers and sisters, do not swear—not by heaven or by earth or by anything else. All you need to say is a simple “Yes” or “No.” Otherwise you will be condemned.
James strongly condemns swearing by members in the early church. Swearing as defined by Webster's dictionary is: "To affirm or utter a solemn declaration, with an appeal to God for the truth of what is affirmed; to make a promise, threat, or resolve on oath; also, to affirm solemnly by some sacred object, or one regarded as sacred, as the Bible, the Koran, etc."
So why is James so adamantly against it. First of all Jesus says something similar in the Sermon on the Mount, where he says, "But I tell you, do not swear an oath at all: either by heaven, for it is God's throne." When someone swears by something God or otherwise, they are trying to make someone think what they are saying is true. They don't trust enough in their yes or no, but want to add more weight to what they are saying. They are usually think of the most powerful entity they can call on to add or give credence to what they are saying. Often God is added in an oath to add extra weight to the statement.
I found this commentary quite helpful on this matter,
"The principle here is clear for Christians: do not make vows, either to the Lord or to one another. First, we are unable to know for sure whether we will be able to keep vows. The fact that we are prone to the errors in judgment which are part of our fallen nature means that we may make vows foolishly and/or because of immaturity. Further, we don’t know what the future will bring—only God does. We don’t know what will happen tomorrow (James 4:14), so to make a vow that we will do or not do something is foolish. God is the one in control, not us, and He “works all things together for good for those who love Him and are called according to His purpose” (Romans 8:28). Knowing this, we can see that it is unnecessary to make vows and indicates a lack of trust in Him. Finally, Jesus commands that our word be sufficient without making vows. When we say ‘yes’ or ‘no,’ that’s exactly what we should mean. Adding vows or oaths to our words opens us up to the influence of Satan whose desire is to trap us and compromise our Christian testimony."
So what does this mean for us? First, I don't think this is talking about profanity. For me it means that we need to be very careful with our vows, whether made in God's name or not. Why? Because when our yes does not mean yes, and our no does not mean no, we have lost credibility. There are many sacred vows we make as in marriage. This is a commitment we make for life to be with another person. We can see each time a person breaks that vow, it easier to do next time. Have you also noticed that one lie makes the next lie easier. And while we think swearing in God's name makes our words more credible, when we lie in God's name we take his name in vain breaking the second commandment.
So God and Jesus warn us against this because it sets us up to not make good on our promises, which diminishes other's ability to trust in our word. And when this happens it is not good. Our word and whether it is trusted or not is one the most important things we need to guard. When we swear by something else, we are saying my own word is not good enough. Actually it is saying my word can't be trusted, so I have to swear by something or someone else.
So let's think before we swear about anything. Let's take the time to consider whether we can say yes, or if it is better to say no than to break our promise.