Speaking to his beloved brethren, James says to “be swift to hear, slow to speak, slow to wrath” (James 1:19). At this point the text’s variants seem to be important. The Revised Version and modern translations add: “You know this my beloved brethren, but…”[1] That is, they know that they had been begotten anew by hearing “the word of truth” (verse-18; the Gospel) that was preached to them. Therefore, James writes be swift to hear “the word of truth” but slow to speak (cp. James 3:1), or perhaps more to the point: ‘don’t be quick to judge’ one another by the word of truth. Be swift to hear the Gospel and apply its judgment upon oneself, but don’t be so quick to require others to measure up to its requirements (cp. James 4:12). In doing so, i.e. by applying the requirements of the Gospel to oneself, but allowing others the freedom to apply its requirements to themselves at their own pace, this will go a long way in helping believers to curb their wrath against one another and, indeed, against all men.
‘You know this,’ so apply it to yourselves, but refrain from holding others into account for your measure of progress, because the judgment and wrath of men do not attain to or work out the righteousness of God’ (paraphrased; James 1:19-20). Jesus told us we shouldn’t resist evil / wickedness (Matthew 5:39). Retaliation, therefore, is never the way to express the righteousness of God, but, remember, we aren’t at this point speaking of defending the innocent against a wicked man or even defending oneself from a would be murderer. The context of James’ letter has to do with persecution over living by the words and deeds of Jesus—the Gospel. In this context, retaliation against one’s persecutor or against the betrayal of a brother would be inconsistent with the love of God. Our example would speak much louder than our words, and the example of peaceful endurance (James 1:3-4) would go a long way to express the righteousness of God in the believer (cp. James 1:20), and bring men’s evil deeds into question by those who witness what is done both by the persecutor and the persecuted.
Therefore, in the context of overcoming evil works with good works (James 1:19-20), Paul puts it thus:
If it is possible, as much as lay in you, be at peace with all men. Avenge not yourselves, beloved, but give place unto wrath: for it is written, Vengeance belongs unto me; I will recompense, says the Lord. But if your enemy hunger, feed him; if he thirst, give him to drink: for in so doing you will heap coals of fire upon his head. Be not overcome by evil, but overcome evil with good. (Romans 12:18-21)
And it is in this context that we need to read James 1:21. If believers are to be an example to others, they need to put away all things that defile a good example. Acting like the world in one’s speech, for example, would tend to detract from one’s overall witness of the truth. If I use harsh language in my communication, it tarnishes any affect good deeds might express. So, everything that defiles the garment of righteousness should be laid aside, not to mention the great wickedness or depravity of evil deeds (James 1:21).
As some scholars interpret it, I believe it would be correct to say James is metaphorically referring to agriculture by mentioning the word of truth (James 1:18) as the engrafted (or implanted) word (James 1:21). In doing so, he would be using filthiness and wickedness as rocks or weeds that hinder the growth of the implanted word, which is needed to grow into a mature life-giving plant (cp. Mark 4:14, 16-19), and therefore an effective witness of the truth.
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[1] The additions appear in the Codex Sinaiticus, the Codex Alexandrinus, the Codex Vaticanus and the Codex Ephraemi Rescriptus.