Do not speak evil against one another, brothers and sisters. Whoever speaks evil against another or judges another, speaks evil against the law and judges the law; but if you judge the law, you are not a doer of the law but a judge. There is one lawgiver and judge who is able to save and to destroy. So who, then, are you to judge your neighbor? (Jas 4.11-12)
It is interesting here to consider the argument that James gives against judging another person. In the first place, he says that to judge a person or speak evil against her is to do to the same things to the law. To my mind he may be referring to the injunction of Christ in the sermon on the mount against judging (Mt 7.1-5). If that is true, then it is fitting that he call the sermon "law," since it was offered with obvious analogy to Moses' reading the Law from the mountain in Exodus.
Now in that law of Christ, we are told not to judge another person. Therefore James infers that if a person judges another, she is simultaneously assuming a position of superiority to the law given by Christ. It is as if by judging another person, you say: Christ, I know better than what you've told me; this person is clearly in the wrong, and I am clearly right to think and speak the way I do. When we refuse to do what Christ tell us and we insist that we are right in doing so, what else are we doing except asserting our own superiority to Christ? affirming that we know better and that Christ's advice is foolish?
Such a person is obviously in competition with Christ, however, who is the only lawgiver and judge who is able to save and to destroy (v. 12). But this Christ with whom we compete whenever we judge is the only one who has risen from the dead, and who has conquered the forces of evil and darkness. He's the only one who was declared Christ, Lord, Son of God in power. If you compete with him, you are destined to lose. That is why James doesn't even bother to follow the chain of inferences much further than this -- viz., to the point that judging another is competition with Christ -- because he has already said enough. If we are Christians, we cannot compete with Christ but must rather submit to him.
The final question is a good one: So who, then, are you to judge your neighbor? Unless you think you have taken on the role of Christ, the only judge of the living of the dead, the only giver of the law that gives life, you have no place judging other persons. It is not your job.
Some Christians like hearing this, others don't. Some Christians like to hear that we are not to judge, and other Christians can't stand hearing it. But the command not to judge ought to be taken wisely. The refusal to judge obviously cannot entail that you say nothing in the face of evil, which would be monstrous. But neither can we incessantly call others to give responses for their actions, even the minutia we find sinful. There must be room for moral rebuke done in love, without an extreme legalism that fails to recognize the distinction between great faults and minor peccadillos, and without a complete refusal to name anything at all as wrong.
Certainly the refusal to judge entails the refusal to name the final destiny of any person. Christ alone determines that; if we as Christians have anything to say about the final destiny, it is that in Christ we have salvation, and we are to call everyone to that salvation. Apart from the call to Christ, we make no further statements.
My friend Bill recently wrote about this here.