The simple lesson to be learned from James 4:11-12 is that Christians must not give in to the temptation of “measuring” others against ourselves. None of us sets the standard against which anyone else is to be evaluated. The “evil speaking” of vs. 11 represents the idea of incriminating someone else, of deliberately (and wrongly) damaging their reputation. James makes it plain that the “evil speaker” is putting himself in the place of God by doing so (vs. 12). Paul also counseled against judging “before the time” when the Lord will make all the facts of every person’s situation known (1 Corinthians 4:5).
Neither James nor Paul is teaching that “all” judging is wrong (as so many try to assert, by misapplying Jesus’ own words in Matthew 7:1). Jesus Himself showed very plainly in John 7:24 that His followers must “judge” in the course of everyday living, but that we must do so according to HIS standard, not our own. What James warns against here is what Paul described in 2 Corinthians 10:12 – “…measuring [ourselves] by [ourselves], and comparing [ourselves] among [ourselves]….”
Similarly, James does not teach in 4:13-17 that “it’s wrong to plan for the future” (such as in buying life insurance, etc.). Rather, his point is that Christians should always make future plans, and choose future paths in this life by first considering our Lord’s will, and how is should “shape” and fit into such plans. Perhaps the stronger point James makes is that Christians should not even make plans that exclude His will! It is in this particular contest that we should pay special attention to the warning of vs. 17, that “…to him who knows to do good and does not do it, to him it is sin.”
Much of James 5 focuses on correcting behaviors that the Jewish Christians may have instinctively (and perhaps unintentionally) “carried over” from Jewish culture into their Christian lives. (These seem to include their attitudes toward wealth and poverty, vv. 1-6, and their perspective on suffering – see Job 8:3 -4 & 22:5, and John 9:1-2 for examples.) It is in connection with these attitudes and ways of thinking about life in this world that James points Christians toward prayer (vv. 13-15 & 17 -18), self-examination that results in the confession of our own offenses (vs. 16), and focused efforts to restore – rather than “judge” – those who do stray into sin.