Let what you say be simply ‘Yes’ or ‘No’; anything more than this comes from evil.
37. But your speech shall be, Yes, yes; No, no Christ now prescribes, in the second place, a remedy; which is, that men act towards each other sincerely and honestly: for then simplicity of speech will have quite as much weight as an oath has among those who are not sincere. Now, this is certainly the best way of correcting faults, to point out the sources from which they spring.
Perjury is impiety toward God and injustice toward man combined; it renders a man obnoxious to divine wrath. The ancients understood this so well they turned their swearing formulas into curses upon themselves, wishing God's judgment if they lied. This shows how deeply nations have always felt that God must curse the false swearer, if He be God.
AI summary
Commenting on Matthew 5:33-37
But let your communication be yea, yea,.... That is, let your speech, in your common conversation, and daily business of life, when ye answer to anything in the affirmative, be "yea"; and when ye answer to anything in the negative, "nay": and for the stronger asseveration of the matter, when it is necessary, double these words; but let no oaths be joined unto them: this...