The following is an excerpt from The MacArthur New Testament Commentary on Matthew 7.

Do not judge lest you be judged. (7:1)Unrighteous and unmerciful judgment is forbidden first of all because it manifests a wrong view of God. With the phrase lest you be judged, Jesus reminds the scribes and Pharisees that they are not the final court. To judge another person’s motives or to curse to condemnation is to play God. “For not even the Father judges anyone, but He has given all judgment to the Son” (John 5:22). During the millennial kingdom Christ will share some of that judgment with us (Matt. 19:28; 1 Cor. 6:2; etc.), but until that time we blaspheme God whenever we take upon ourselves the role of judge. “Who are you to judge the servant of another?” Paul asks. “To his own master he stands or falls” (Rom. 14:4). Paul was little concerned about how other people judged him, and was not even concerned about how he judged himself. “I am conscious of nothing against myself,” he says, “yet I am not by this acquitted; but the one who examines me is the Lord” (1 Cor. 4:3–4).

Except as they may be continually teaching false doctrine or following standards that are clearly unscriptural, we are never to judge a person’s ministry, teaching, or life-and certainly not his motives-by a self-styled standard “Do not speak against one another,” James warns us. “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 of it. There is only one Lawgiver and Judge, the One who is able to save and to destroy; but who are you who judge your neighbor?” (James 4:11–12). Such evil judgment is blasphemous, because it sets a man up as God-and there is only one true Judge.

Whenever we assign people to condemnation without mercy because they do not do something the way we think it ought to be done or because we believe their motives are wrong, we pass judgment that only God is qualified to make. An unknown poet of past days wrote,    Judge not the workings of his brain,
    And of his heart thou cannot see.
    What looks to thy dim eyes a stain,
    In God’s pure light may only be
    A scar brought from some well-won field
    Where thou wouldst only hint and yield.The Savior does not call for men to cease to be examining and discerning, but to renounce the presumptuous temptation to try to be God.