10 Yet I certainly did not mean with the sexually immoral people of this world, or with the covetous, or extortioners, or idolaters, since then you would need to go out of the world. 11 But now I have written to you not to keep company with anyone named a brother, who is sexually immoral, or covetous, or an idolater, or a reviler, or a drunkard, or an extortioner--not even to eat with such a person. 12 For what have I to do with judging those also who are outside? Do you not judge those who are inside?
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!