Its been a while...
Paul wrote to the Romans,
"As for the one who is weak in faith, welcome him, but not to quarrel over opinions. One person believes he may eat anything, while the weak person eats only vegetables. Let not the one who eats despise the one who abstains, and let not the one who abstains pass judgment on the one who eats, for God has welcomed him. Who are you to pass judgment on the servant of another? It is before his own master that he stands or falls. And he will be upheld, for the Lord is able to make him stand." (Romans 14)
He also wrote this to the Corinthians,
"It is actually reported that there is sexual immorality among you, and of a kind that is not tolerated even among pagans, for a man has his father's wife. And you are arrogant! Ought you not rather to mourn? Let him who has done this be removed from among you. For though absent in body, I am present in spirit; and as if present, I have already pronounced judgment on the one who did such a thing. When you are assembled in the name of the Lord Jesus and my spirit is present, with the power of our Lord Jesus, you are to deliver this man to Satan for the destruction of the flesh, so that his spirit may be saved in the day of the Lord. Your boasting is not good. ... I wrote to you in my letter not to associate with sexually immoral people-- not at all meaning the sexually immoral of this world, or the greedy and swindlers, or idolaters, since then you would need to go out of the world. But now I am writing to you not to associate with anyone who bears the name of brother if he is guilty of sexual immorality or greed, or is an idolater, reviler, drunkard, or swindler--not even to eat with such a one. For what have I to do with judging outsiders? Is it not those inside the church whom you are to judge? God judges those outside. "Purge the evil person from among you." (1Corinthians 5)
Is Paul confused? One letter tells us not to judge one another. Another letter tells us to publicly judge and discipline those that are walking in blatant, unrepentant sin. It seems like most people want to cling to one of these passages and ignore the other. One group wants to judge everything in sight, and the other wants to turn a blind eye to the sin that will destroy both the church and the individual, in the name of compassion. I am pretty confident that the Lord doesn't give us that option. So, how do we know when to judge and when not to?
I think, based on these two passages, it has to do with the subject matter. Sexual immorality of any kind, stealing, lying... these are all behaviours that are obviously wrong. There is no gray area here, and they are clear violations of God's moral law. We are no longer under the law as the means by which we are saved, but it is still true as His declaration of right and wrong, and what is best for us. Based on Paul's message to the Corinthians, we are in danger of eternal judgment if we continue in willful practice of that which is clearly in rebellion against the truths of that law. If that be true, then love requires us to confront the one in sin and call them to repent. And, according to Paul, if they refuse we must not allow them to fellowship with the church. In the spirit realm he even went so far as to turn them over to Satan to motivate them to wake up and return to the Lord. That's some pretty serious judgment, and Paul rebukes that notoriously carnal church for their lack of willingness to carry it out. This commitment to the holiness and purity of the church is not presented as an option.
On the other hand, there are areas of life that are not black and white before the Lord. Regarding these, he says to the Romans, "Who are you to pass judgment on the servant of another? It is before his own master that he stands or falls. And he will be upheld, for the Lord is able to make him stand." It seems like a contradiction. We go from a command to judge strongly to instructions to refrain from judging completely. Which is it? Again, its all about the subject matter. Paul is talking about matters that are open to debate and personal conviction. What we should eat and when we should worship. There are groups who feel strongly about issues such as these that are "non-essential". They often look with disdain on those who don't have the same revelation they have. They judge them as not being quite as righteous as they are. On the other side, you have those who disagree with the other group's conviction, and look upon them as "in error" or legalistic. Both are wrong and damaging the unity of the church's love. Both are in pride rather than the humililty that Jesus demonstrated and calls us to.
It is interesting to note that we are accountable in these "gray" areas to our own conscience. "The faith that you have, keep between yourself and God. Blessed is the one who has no reason to pass judgment on himself for what he approves. But whoever has doubts is condemned if he eats, because the eating is not from faith. For whatever does not proceed from faith is sin." (Romans 14:22-23)
The question is not whether we should judge or not. There is a time and a place for both. The issue is learning to discern from the Holy Spirit what is appropriate for the situation we find ourselves in. Is this a black and white violation of God's law, or is it a matter of personal conviction? When we gain that understanding, we simply need to obey in the faith that works through love.