The Bible teaches that churches are to judge themselves, restoring those who fall in sin and not keeping company with those who refuse. According to the Bible, if a church does not do this, the Lord chastises the church. Chastisements can include sickness and death ('sleep'.)
I Corinthians 5 teaches that sin spreads like leaven if not dealt with. Therefore, cut off the immoral brother. Hebrews 12 warns that a root of bitterness springing up may defile many, and gives a fornicator as an example.