‘Do not speak one against another, brothers.'
The idea here is that they ought not to speak against one another critically or in condemnation, often without being aware of the facts. Thereby they could do them great harm, both personally, and in the eyes of others. Many an innocent man has been personally destroyed, or has had his reputation destroyed, by malicious tongues. Once again we are being reminded of the importance of controlling the tongue (James 3:1-12), of what causes wars and fightings among men (James 4:1), and of the need to be humble (James 4:10), that is, to be meek and lowly in heart (Matthew 11:29). For those who speak against their brothers are guilty of misuse of the tongue, and of stirring up a violent response and of exalting themselves in comparison. And as we shall see, he points out that it is also wrong because it is to put those who so speak in the place of God. The thought here is not that of avoiding giving loving assistance to a brother (Matthew 7:5; Galatians 6:1-2) but of being censorious and unhelpful and being guilty of harsh judgment and condemnation. It is a matter of balance and motive, and in such matters we are to be swift to hear, and slow to speak (James 1:19). ‘He who speaks against a brother, or judges his brother, speaks against the law, and judges the law. But if you judge the law, you are not a doer of the law, but a judge.'
And one reason why no man should speak against another and set himself up as judge is because by doing so they are speaking against the Law and judging the Law. But we might ask, why should that be so? And the answer is, because of what the Law teaches which by their activities they are refuting. He has told us, for example, that we should not be ‘talebearers' (Leviticus 19:10). If we then disobey this we are passing judgment on the Law that it is wrong and does not apply to us. The same applies to passing judgment on all those parts of the Law which stress love and mercy, such as, ‘You shall love your neighbour as yourself' (Leviticus 19:18). We would not like to be judged by others ourselves, and so we should also avoid judging others. And thus by judging others we are passing a verdict against that Law. We are saying that it is unworkable and not to be observed. But rather than doing that we should approach all with love and sympathy. (Of course if they are blatantly and unrepentantly openly scorning the Law that will be a different matter. Then it will be God Who is passing judgment. But that is not the question that is being dealt with here).
‘But if you judge the law, you are not a doer of the law, but a judge.' The point here is that those who are doers of the Law and those who are judges of the Law take up a totally different attitude. The judge is concerned with judging, not with doing. But they have to be concerned with doing. Thus they exclude themselves from being judges. They are no longer impartial.