There is a lot of misunderstanding among Christians about whether it is right to judge others or not - because of a misunderstanding of the word "judge".
As believers, wemustjudge others in the sense that we must discern people. God's Word says that, when we listen to someone preaching, we "must pass judgement on his message" (1 Cor.14:29). So the Holy Spirit actually commands us to judge everyone's preaching. That is the only way we can avoid being deceived by many deceiving preachers in Christendom today.
The Word of God also says, "Do not believe every spirit, but test(judge) the spirits to see whether they are from God, because many false prophets have gone out into the world" (1 John 4:1).
Jesus also told us how we are to judge others. He said, "Be honest in your judgment and do not decide superficially and by appearances, but judge fairly and righteously" ( John 7:24 - Amplified).
So what did Jesus mean then, when He also said, "Do not judge " (in Matt.7:1 )?
The word "judge" also means "condemn" (in the original Greek). The Amplified Bible translation of this verse reads thus: "Do not condemn others lest you yourself be condemned " (Matt.7:1- Amplified).
And Jesus said, concerning Himself, "I do not condemn or sentence anyone" ( John 8:15 - Amplified).
So it is condemning and sentencing others (verbally or in our mind) that is forbidden.God alone has the right to do that.
But we must test and discern.
It was prophesied about Jesus that He would never judge anyone "by what His eyes saw or His ears heard, but would judge people righteously "(Isa.11:3,4). We should also follow His example and never judge anything or anyone merely by what we see or hear. We should investigate a matter thoroughly and then judge fairly in righteousness, without any partiality.
We are also told, as members of God's family, that we must judge ourselves first (1 Pet.4:17). But weare not to judge ourselves by looking inside ourselves. No. We are to look at Jesus' Example and in the light of His life, see our own shortcomings - and then judge ourselves. As it is written, "Lord, in Your light , we will see light" (Psa.36:9).
Judging ourselves in the light of God is one of the most important lessons that we must learn in the Christian life. Many never learn this and so they never make any spiritual progress.
Here is an amazing promise, that those who judge themselves faithfully now will not be judged by God in the final day: "If we judge ourselves rightly, we will not be judged" (1 Cor.11:31).
Although we do not judge others, we must preach strongly against sin. Jesus spoke strongly against specific sins such as anger, lusting sexually with one's eyes, loving money, anxiety, fear, evil thoughts, telling lies, seeking man's honour, hatingone's enemies, etc. (in Matt.5 ,6and 7 ). We must also speak against modern sins such as watching Internet pornography - but without condemning people. Jesus did not come to condemn the world but to save the world (John 3:17). God alone is the Judge and Sentencer of all men (James 4:12).