From the same mouth come blessing and cursing: this emphasizes and makes clearer the problem that James has referred to in verse 9. It is interesting to note that he shifts from the “tongue” to the mouth, both of which are essential for speech. It is possible that his words may be echoing Jesus’ teaching about the defilement of speech (Matt 15.11, 17-18). In any case what James wants to convey is that doubleness in speech is not right and therefore must be rejected.

My brethren is not used here as a marker for the introduction of new subject matter, as it is in some other places. Here it is used for emphasis, as the author tries to make a passionate appeal to his readers. The address is meant to be inclusive and therefore may be rendered “My brothers and sisters” (New Revised Standard Version), or even “my friends” (Good News Translation, Revised English Bible). (See 1.2 for a further discussion on this expression.)

This ought not to be so is a rare expression; the sentence is literally “It is not fitting, my brethren, that these things should so be” (Hort). The impersonal verb translated “it is fitting” appears only here in the New Testament. Its original sense is apparently “there is need,” and in ethical applications it takes on the meaning “it is fitting” or “it ought to be.” The negative not in Greek is in emphatic position. To bring the force out properly, we may render the statement as “surely, my brothers, this is the sort of thing that never ought to happen!” (Phillips), or even “No, my brothers and sisters, this ought not to be so.” Contemporary English Version combines verses 9 and 10 in order to eliminate some of the repetition that is not good style in modern English. A similar alternative translation model is the following:
• My dear fellow Christians, we use our tongues to speak both praises and curses. We praise our Lord and Father and call down curses on our fellow human beings whom God created to be like himself. We should not do this!

Quoted with permission from Loh, I-Jin and Hatton, Howard A. A Handbook on The Letter from James. (UBS Handbook Series). New York: UBS, 1997. For this and other handbooks for translators see here .