To judge means to personally evaluate someone and find them guilty or to criticize another for something when we have neither the authority, knowledge, or moral strength to do so. The verb most often used is κρινω krino, Strongs #2919, to select, find fault with, criticize, express and opinion, pass judgment. Holding differing opinions is not judging.
We should not self righteously judge or condemn another person whom you think is wrong or sinning. Quite often the one judging is self righteous. He thinks he is quite moral, while others are below him, when in fact, he also sins. This kind of person is critical, self righteous, and pushy. Furthermore, we are not to express this judgment to someone else. Judging begins with an attitude and often shows up in expression, words, or action (Matthew 7:1-5; Luke 6:36-37; Romans 2:1; Romans 14:1-13; 1 Corinthians 4:5; Colossians 2:16-17; James 4:11-12).
When we criticize and judge, we are admitting to a standard in our conscience, and we often break that standard ourselves. And in effect, we are also condemning ourselves for the same or similar sin. Romans 2:1, “You condemn yourself” is the verb katakrino κατακρίνω, to pass sentence after determining guilt. Matthew 7:1-2 “Do not judge so that you will not be judged” has the verb κρινω krino. John 8:1-11 is the illustration of the scribes and Pharisees self righteously judging the adulterous woman, and Jesus corrects them.
To recognize wrong is not judging. We are instructed to know the difference between right and wrong. Jesus, in John 7:24, said to those who did not know the facts and wanted him dead “judge with righteous judgment.” We are to evaluate and distinguish good from evil, Hebrews 5:14 διακρισις diakrisis to distinguish, evaluate. See also 1 Corinthians 5:12; 10:15,29; 11:13; and Acts 16:15. All use the verb κρινω krino. John instructs in 1 John 4:1 to think and evaluate and so do not believe everyone who says “God has spoken to me,” δοκιμαζω dokimazo to make a critical examination, test. To fulfill Matthew 7:6,15 we need to know who is a pig and who is a false prophet. The nobleman in Luke 19:11-27 had the authority, knowledge, and courage to judge (Luke 19:22 κρινω krino). In John 7:50-51, Nicodemus had the authority and knowledge to speak to the Pharisees (κρινω krino). In Acts 26:6, Paul is on trial before Agrippa and Festus where Agrippa had the authority (κρινω krino). In 1 Corinthians 5 Paul corrects the church for not judging a public and ongoing sin (1 Corinthians 5:12 (κρινω krino). But we are not to act as a prosecutor and judge of someone else except in rare situations and only when we have the authority, knowledge, and moral courage.
If someone is clearly wrong, then you make an evaluation and you may separate, but do not condemn. Even separation is to help restoration (2 Thessalonians 3:14; 1 Corinthians 5; 2 Corinthians 2:5-11). It is God’s responsibility to deal with it by himself or through proper authority.
Finally, remember, we may have differing opinions. Do not critically judge others about non essential or biblically neutral things such as food, drink, special days (Romans 14:1-13; Colossians 2.16-17), or how they serve the Lord (1 Corinthians 4:1-5).