Should I Separate from Sinful People in My Church?

If a person in your church lives a sinful lifestyle and is a leader, how should I respond to that person? Should I sit under their teaching and leadership? Should I separate from sinners in the church? A lady asked, “I know I am to engage sinners for redemptive purposes because that is what Christ did to me. I don’t want to separate from them but influence them with the gospel. But what about the ongoing sinfulness of someone in your church?”