What is the purpose of shunning or ostracizing a believer who is living in sin?
The purpose is not to be nasty but to let God's discipline come home to a sinning believer. Scripture admonishes believers not to fellowship with those who claim to be believers yet persist in sin; ostracizing them for a while, while explaining why, aims to awaken them to their wrongdoing.
Les explains that the purpose of shunning or ostracizing a sinning believer is not to be purposely nasty. If a person has been genuinely saved, even though he goes out into sin, and the Lord has not yet taken him out, way down deep he is miserable and cannot be happy. The Lord is dealing with him, and when fellow believers shun him, it really comes home. God has a reason for this: believers are told to ostracize such acquaintances for a while, but let them know why, because Scripture admonishes us not to have fellowship with those who claim to be believers yet live that way. This is not about the lost world; Paul says he has no authority to judge those outside. It is practical, everyday living for believers.