Matthew 5:34-35,37 But I say to you, do not swear at all, either by heaven, for it is the throne of God, or by the earth, for it is His footstool, or by Jerusalem, for it is the city of the Great King…Let what you say be simply “yes” or “no”; anything more than this comes from evil.
There is power in the name of the Lord Jesus. As such, we should not treat His name as just another word. Throwing around the name of our Savior is to use His name in vain. To make an oath by swearing to God cheapens His name. Besides that, though, as followers of Christ, we should not need to swear by anything for our oath to mean something.
This isn’t a legalistic command to refuse taking an oath. It’s a call to live our lives with character. We should live and practice truth, so much that just saying “yes” or “no” would be taken as an honorable oath.
In order for our yes to be yes, we must give no one reason to believe that we would lie to them. We must live a life set apart from the lies that permeate this world. We’ve got to have character that is so above reproach that there’s no reason to question our honesty. Give no reason for anyone to doubt your word. By doing so, you bring honor to God.