Simply let your ‘Yes’ be ‘Yes,’ and your ‘No,’ ‘No.’ Anything more comes from the evil one.
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.
We have here an exposition of the third commandment, which we are the more concerned right to understand, because it is particularly said, that God will not hold him guiltless, however he may hold himself, who breaks this commandment, by taking the name of the Lord in vain. Now as to this command, I.
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...