But let your word be, Yes, yes; No, no; for anything more than these is of the evil one.
Our words should be brief and clear. Those who are honest do not talk very much. But beware of talkative people: they may be liars. Liars are very talkative, always giving many reasons and excuses for things. But an honest person is usually brief. Furthermore, we must realize that much talk in the presence of God does not make the Lord happy. When we go to the Lord, we must go to Him in honesty, saying things to Him in a brief way.
In verse 37 the Lord says that whatever is more than a straight yes or no is of the evil one. Here we come to a crucial point: in our talking the evil one may be present. When we speak more words than are necessary, those words are not of us, but of the Devil, the evil one.