10 But I wasn't talking about unbelievers who indulge in sexual sin, or are greedy, or cheat people, or worship idols. You would have to leave this world to avoid people like that. 11 I meant that you are not to associate with anyone who claims to be a believer yet indulges in sexual sin, or is greedy, or worships idols, or is abusive, or is a drunkard, or cheats people. Don't even eat with such people. 12 It isn't my responsibility to judge outsiders, but it certainly is your responsibility to judge those inside the church who are sinning.
Matthew Henry's Commentary on 1 Corinthians 5:10-12
Commentary on 1 Corinthians 5:9-13
(Read 1 Corinthians 5:9-13)
Christians are to avoid familiar converse with all who disgrace the Christian name. Such are only fit companions for their brethren in sin, and to such company they should be left, whenever it is possible to do so. Alas, that there are many called Christians, whose conversation is more dangerous than that of heathens!