Let what you say be simply “Yes” or “No” is literally “But let your word be ‘yes, yes’ or ‘no, no.’ ” In light of a similar passage in James 5.12 and the interpretation given this verse in the early church, the meaning is that every “Yes” must be simply “Yes,” every “No” simply “No.” The translations concur with this conclusion: New International Version (New International Version) “Simply let your ‘Yes’ be ‘Yes,’ and your ‘No,’ ‘No’ ”; Barclay “when you mean yes, say yes—nothing more; when you mean no, say no—nothing more”; New Jerusalem Bible “All you need say is ‘Yes’ if you mean yes, ‘No’ if you mean no.”
The examples of Barclay and New Jerusalem Bible have proved particularly helpful as models to translators. But it is important that the translation does not seem to be talking about ways of answering questions. Rather, Jesus is still discussing affirming that one will or will not do something. Therefore one possible translation is “When you are going to do something, just say yes, you will do it, or no, that you are not going to do it.”
Evil (Anchor Bible “of evil origin”) translates a noun which may be either neuter or masculine (Good News Translation “the Evil One”; so also New Jerusalem Bible, Barclay, New American Bible, New International Version, RSV footnote; New English Bible, Die Bibel im heutigen Deutsch “the devil”). The same ambiguity exists in 5.39; 6.13; and 13.38. Scholars argue in both directions. For example, one commentator believes “evil” to be the more likely translation, even though in 13.19 the reference must be to “the Evil One” in light of the parallel with Mark 4.15, which has “Satan.” Another commentator argues in favor of “the Evil One” on the basis of 19.17, where God is referred to as “the Good One.” This interpretation, “the Evil One,” seems to satisfy best the demands of the present context.
The words anything more refer to adding to your declaration any confirmation or guarantee beyond your own word. The feeling that you need to do this comes from, that is, “is inspired by the Evil One,” “is caused by…,” or “has as its source….”
“The Evil One” is not always easily understood. Translators may say “that One who is the source of evil” or “the Devil, who is the Evil One.”
The last part of this verse may be restructured as “The idea that you need to say any more (or, do more than give your word) comes from the Devil, the Evil One,” “It is the Devil, who is the Evil One, who makes you think you need to do more than that when you declare something true,” or “Any statement more than that is caused by the Evil One, the Devil.”
Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on the Gospel of Matthew. (UBS Handbook Series). New York: UBS, 1988. For this and other handbooks for translators see here .