The Apostle Paul
1 Corinthians 5:11ESV·traditional attribution

But now I am writing to you not to associate with anyone who bears the name of brother if he is guilty of sexual immorality or greed, or is an idolater, reviler, drunkard, or swindler—not even to eat with such a one.

John Calvin Reformed @genevareformer

11. If he who is called a brother In the Greek there is a participle “Au texte Grec il y a de mot a mot, Si aucun frere nomme,” etc.; — “In the Greek text it literally, If any one, called a brother,” etc. without a verb. It is so according to the common reading, which is as follows: — ἐάν τις, ἀδελφὸς ὀνομαζόμενος, ἣ πόρνος, ἣ πλεονέκτης, κ. τ.

Matthew Henry Presbyterian @wholebiblehenry

Here the apostle advises them to shun the company and converse of scandalous professors. Consider, I. The advice itself: I wrote to you in a letter not to company with fornicators, Co1 5:9. Some think this was an epistle written to them before, which is lost.

Commenting on 1 Corinthians 5:9-13

John Gill Reformed Baptist @doctorgill

But now have I written unto you,.... Which shows, that what he had written before was at another time, and in another epistle; but not that what he was now writing was different from the former, only he explains the persons of whom, and the thing about which he has before written: not to keep company, if any man that is called a brother, be...