James 5:12 (KJV) “But above all things, my brethren, swear not, neither by heaven, neither by the earth, neither by any other oath: but let your yea be yea; and your nay, nay; lest ye fall into condemnation.”
James has just written about how to deal with trials and temptations through patients and endurance. In the next verses James explains how to handle specific circumstances.
The first is a command to never swear neither by heaven nor by earth. Today Christians have a cute way of substituting words for actual curse words but God still knows the intent of the heart. We have already been commanded not to speak ill of our brothers and we need to watch our tongues.
The most important thing is to not have to make an oath pledging to do something. We should lead a life that is exemplary and always mirrors Jesus. By doing this when we make a statement people will trust what we say. We need not make an oath, because if our word alone is not enough we as Christians have missed the mark.