If, and only if your brother (here Jesus is refering to someone who claims to be a Christian) repents are you to forgive him (or her).
But does this not contradict what Jesus taught else where?
For if you forgive men when they sin against you, your heavenly Father will also forgive you. But if you do not forgive men their sins, your Father will not forgive your sins (Matt 6:14,15).
What are we to do? Forgive or not forgive? Jesus seems to be contradicting himself, but is he?
There are two types of forgiveness in the Bible and both can be practiced similtaneously.
One type simply means to do our best for the person who has sinned no matter what they think of us or have done to us. We are to love them unconditionally. (Love your enemies. see Matt 5:43,44.) If I am trying to help someone and not trying to destroy them you would have to conclude that I have forgiven them. This kind of forgiveness simply means to love unconditionally. The other type of forgiveness is conditional. There will be occasions, when if we are to show love toward someone who claims to be a Christian, we must not act as though what they have done makes no difference. Love can be tough (see 1 Cor 5:1-2). Choosing not to forgive is sometimes the most loving thing we can do, as it will help an unrepentant Christian to see the seriousness of their sin. (See also hate)
Matthew 18:15-35 illustrates both types of forgiveness and how conditional forgiveness is to be exercised. (These particular verses are often misunderstood. See Postmodern Bible Study by Chuck Edwards for the correct exegesis of these verses.)
Obviously if the process that Jesus outlines is followed it could lead to excommunication (as 1 Cor 5:1,2 illustrates). It is important to note that it is not the senior pastors role to excommunicate people. Jesus outlined a process and that process should be followed.
The role of senior pastors itself should be looked at closely. The famous Chinese pastor, Watchman Nee, believed that the book of Acts gave no support for the idea of a senior pastor. The churches he established had no senior pastor, each was governed by its own group of elders. J.P. Moreland also believes that there is no biblical basis for senior pastors. He argues his case in part 3 of Loving God with your mind. It is worth thinking about how different history may have been with no individuals controlling churches or groups of churches. What abuses of power might have been prevented if there were no senior pastors or ruling bishops? Not only would history be different but today's churches would be very different. How many pastors have children who do not obey them but they get to keep their positions because there is no one to replace them? (See 1 Tim 3:1-5) At the time of the book of Acts churches did not have this problem because there were multiple bishops (elders) in each church.
Excommunication raises doubts in the minds of many believers. Perhaps you are one of them. You might be thinking. "How do I know that I forgiven my brother (or sister) in the way that Jesus would have me forgive them? Jesus said that if I don't forgive, God won't forgive me." It is easy to see if I have forgiven or not if I ask myself the following questions. "What do I desire for this person? Am I willing to help them? Do I want to see them repent or do I want to see them destroyed?" (See Hate & Judge)
Question:
If we are to forgive, how should a Christian judge treat a criminal? See But Jesus would forgive by Greg Koukl.
