James goes on to set up a contrast between a person who is meek and one who is jealous and ambitious, and he introduces the contrast by a pair of conjunctions, But and if.

The pair of terms in Greek for jealousy and selfish ambition appears in Paul’s lists of vices (translated “jealousy” and “selfishness” in 2 Cor 12.20; Gal 5.20). The word rendered jealousy, literally “zeal,” was originally a neutral term. But the predominant meaning in the New Testament is the negative sense of a desire to promote your own opinion from a selfish motive. It is a zeal that is fanatical (Barclay), and therefore may be rendered as “envy” (Translator’s New Testament, New International Version, New Revised Standard Version). James qualifies jealousy with the adjective bitter, thus intensifying the feeling of a contentious spirit, in contrast to humility and gentleness. Bitter in this context means “biting,” “intense,” or “severe.” Some other ways to express bitter jealousy are: “a heart full of intense jealousy,” “have a heart hot with jealousy,” or “have an inordinate desire to get what other people have.” Selfish ambition, one word in Greek, is a rare word sometimes used of the attitude of greedy politicians putting their own interests above everything else, often resulting in rivalry and partisan spirit. It may therefore be rendered as “spirit of rivalry” (Traduction œcuménique de la Bible, Bible en français courant, Revised English Bible). We may also express it as “desire to be better than others.” In some languages this is described idiomatically in terms of the heart; for example, “have a black heart,” or “have a narrow heart.” As James sees it, the problem of jealousy and rivalry is not external, it is in your hearts, the inner feelings a person may have that are not publicly known. For the meaning of hearts see the discussion in 1.26.

In spite of the fact that the verse begins with the conditional clause But if you have …, the prohibition do not boast remains valid, whether or not the condition is realized. In other words boasting and lying are wrong and should be prohibited, whether they spring from jealousy and ambition or not.

Do not boast and be false to the truth: the meaning of this prohibition is not very clear. To boast is to praise oneself, especially in comparison with someone or something else, thus to have “pride” (Goodspeed) or to “brag” (Contemporary English Version). But what is the object of bragging? There are a number of possibilities.
(1) The first possibility is to take the verb boast absolutely without any object, referring to a person’s attitude and disposition. In this case the negative not goes with both verbs, and a comma or period is usually placed after the verb boast to separate the two clauses (so Japanese colloquial version), making boasting and lying two actions. This is seen in the renderings like “glory not, and lie not against the truth” (King James Version), and “do not be boastful, nor lie against the truth” (so CUV, Japanese New Interconfessional Translation). The boasting is sometimes understood in relation to others (for example, “you must not treat others with arrogant conceit” [Barclay]), and sometimes in relation to yourself (thus “do not make false claims for yourselves” [Translator’s New Testament]).
(2) Another possibility is to take the truth as the object. In this case the truth is understood to be the object of both verbs, to boast and to be false to. This would probably be the assumed meaning for ordinary readers who follow a literal rendering like that of the Revised Standard Version. In this case what James is saying appears to be “Do not be boastful about the truth or lie against it.” Contemporary English Version expresses this as “Don’t brag or lie to cover up the truth.”
(3) Still another possibility is to take the truth as the object, but to interpret do not boast and be false to the truth as a hendiadys, that is to take boasting and lying to be one idea or event. This is reflected in a rendering like “stop making false claims in defiance of the truth” (Revised English Bible).
(4) One more possibility is to take wisdom in verse 13 as the object of boasting. This is seen in renderings like “do not boast about it or deny the truth” (New International Version), and “do not pride yourselves on it and thus belie the truth” (Goodspeed). The pronoun “it” in both cases most likely refers back to “wisdom.” What James is saying here, then, would be that unjustifiable boasting about wisdom will result in denying or lying against the truth.
(5) A final possibility is to identify “wisdom” as the object of the verb “to boast” and to take the boasting of wisdom as the means of lying against the truth. This interpretation is seen in the Good News Translation rendering, “don’t sin against the truth by boasting of your wisdom.” Boasting about wisdom while being jealous and ambitious is, in fact, lying or sinning against the truth. This interpretation appears to fit the context best, and in fact makes the best sense, and is therefore the option recommended by this Handbook.

The expression be false to the truth appears redundant to some people if the truth is understood as “truthfulness.” For this reason some scholars suggest that the truth should be taken in the objective sense of “the truth revealed through Christ,” namely the gospel, or the Christian faith. It is also possible, however, to take it as referring to that which is true and real as against that which is false and unreal. James’ thinking then is this: “True wisdom is associated with humility. This is the truth. If so, to boast about wisdom when you are jealous and ambitious is a contradiction in terms; it cannot be true.” This is supported by what James goes on to say in the next verse.

The following alternative translation for verses 13 and 14 will bring this meaning out clearly:
• Are any of you truly wise? If you are, you must show it by living a right life and by being humble and wise in everything you do. This is true wisdom. But if you have a heart full of jealousy and a desire to be better than other people, you must not boast that you are a wise person [or, have spiritual understanding]. If you do that you turn what is true into a lie.

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 .