12 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.
This one verse appears to be out of place in the middle of James 5. It is tied in with judging however. The idea behind it is simply that Christians should be careful about what they say and how they say it.
Jesus offered very similar instructions when he condemned the Pharisees for many of their practices in Matthew 5:33-37:
33 “Again, you have heard that it was said to the people long ago, ‘Do not break your oath, but fulfill to the Lord the vows you have made.’ 34 But I tell you, do not swear an oath at all: either by heaven, for it is God’s throne; 35 or by the earth, for it is his footstool; or by Jerusalem, for it is the city of the Great King.36 And do not swear by your head, for you cannot make even one hair white or black. 37 All you need to say is simply ‘Yes’ or ‘No’; anything beyond this comes from the evil one.
The idea that both Jesus and James propose is that we shouldn’t need to swear by anything. Christians should be people of integrity and we should be known as people of integrity. This means that our word is good enough because we will stand by our word.
Of course in our world we no longer can do business based solely on our word or a handshake agreement. At times we must enter into formal contracts whether that is a work agreement or a loan. These are necessary things in these times because many people are unscrupulous and cannot be trusted to keep their word.
In our regular dealings with people however, we should have no need to swear because there is really nothing that we can swear by. We have control over so little in life and even that truly belongs to the Lord. Because of this, we should simply speak the truth without need to swear by anything, letting our yes mean yes and our no mean no.