Video from Desiring God
"Rebecca emails in to ask a question about church discipline. She asks, “In regards to Matthew 18:15–20, I am wondering what I as a Christian am responsible to do biblically when a fellow believer is living in sexual sin and chooses to continue after they have been confronted in a loving way.”
The practical answer here really does depend on whether Rebecca and the person she is concerned about — maybe a friend who is sleeping with a boyfriend, I don’t know what her situation is, but let’s just say something like that — whether those two people are in a biblically faithful church. That is, a church that considers the Bible as their standard of faith and practice. And if they are, the answer is or should be: yes, excommunication can and maybe should happen..." from transcript link.