"For I indeed, as absent in body but present in spirit, have already judged (as though I were present) him who has so done this deed. In the name of our Lord Jesus Christ, when you are gathered together, along with my spirit, with the power of our Lord Jesus Christ, deliver such a one to Satan for the destruction of the flesh, that his spirit may be saved in the day of the Lord Jesus."
1 Corinthians 5:3-5 (NKJV)
Secondly, it is right for the Church to deal with unrepentant sinners.
One area the Church has been given the go-ahead and authority by God to judge others is in matter of serious sin within the Church. In the Church at Corinth there was a serious sin that was being left unchecked by the Church, indeed the Church was boasting that such a thing was happening as they thought it showed their true freedom in Christ.
As bad as it may seem to us, one of the Church brothers was actually having sexual relations with his "father's wife" (v1). The Corinthians were deluded into thinking this should not be judged as they bought into the Spiritual Urban Legend we are currently looking at. Paul wrote back saying that he had judged the situation and so should they. They should judge this brother as Jesus clearly taught the Church to do in Matthew 18:15-17:
"Moreover if your brother sins against you, go and tell him his fault between you and him alone. If he hears you, you have gained your brother. But if he will not hear, take with you one or two more, that 'by the mouth of two or three witnesses every word may be established.' And if he refuses to hear them, tell it to the church. But if he refuses even to hear the church, let him be to you like a heathen and a tax collector." (NKJV)
As we have see, there are times the Church must rise up to judge as that is our destiny in Christ, to be judges and rulers. But it must be righteous judgment where we have the moral authority. In such cases where there is obvious sin the Church must not turn a blind eye, but turn a non-hypocritical eye of judgement towards the situation.
When a Christian brother or sister clearly sins against you, you must firstly confront them one on one and seek reconciliation. You extend forgiveness to them but if they reject you bring in two or three more mature counsellors. If this fails the matter needs to be brought before the whole church (through the leadership) and be dealt with accordingly. This may even lead to the Christian being ex-communicated from the Church (notice the purpose of this is still restorative - we are to treat them as non believers, ones we are to reach out to in love).
Notice that this is in the context of the Church. If non-believers sin against Christians then the Christians should immediately forgive them and shine forth the love of Christ. What is the point of a Christian judging a non-Christian when they are already under eternal damnation without Christ! The Christian's role towards the non-believer is to declare the Good News about Jesus Christ.
The Church often judges when it should not,
And fails to judge the creeping rot,
The sin that's so often is left unchecked
So that many believers end up ship wrecked!
"Father, help me to judge when I have the moral authority to do so. That means pointing out my brothers of sisters sin so they an repent and be restored. Give me the boldness to be a righteous judge when I need to be. Amen."