Charles Ellicott Commentary Matthew 5:37

"But let your speech be, Yea, yea; Nay, nay: and whatsoever is more than these is of the evil [one]." — Matthew 5:37 (ASV)

Let your communication—This is one of the few instances in which the translators seem to have preferred a somewhat pedantic Latin word over the more literal and simple English word speech. .

Yea, yea—Saint James reproduces the precept in his epistle (James 5:12), but the phrase is also found in the Talmud and was likely proverbial. In all common speech, a person’s words should be as good as their oath. Yes should mean yes, and No should mean no, even if there is no oath to strengthen it.

Cometh of evil—The Greek may (as in the Lord’s Prayer, Deliver us from evil) be either neuter, “from evil in the abstract,” or masculine, “from the evil one.” With some hesitation, and guided chiefly by Matthew 13:19-38, I accept the latter as the more probable. These devices of fanciful oaths do not come from Him who is the Truth, but from him who when he speaketh a lie, speaketh of his own (John 8:44).