I wrote unto you in an epistle not to company with fornicators:
All Commentaries on 1 Corinthians 5:9 Go To 1 Corinthians 5
For since he had said, You have not rather mourned, that such an one should be taken away; and, Purge out the old leaven; and it was likely that they would surmise it to be their duty to avoid all fornicators: for if he that has sinned imparts some of his own mischief to those who have not sinned, much more is it meet to keep one's self away from those without: (for if one ought not to spare a friend on account of such mischief arising from him, much less any others;) and under this impression, it was probable that they would separate themselves from the fornicators among the Greeks also, and the matter thus turning out impossible, they would have taken it more to heart: he used this mode of correction, saying, I wrote unto you to have no company with fornicators, yet not altogether with the fornicators of this world: using the word altogether, as if it were an acknowledged thing. For that they might not think that he charged not this upon them as being rather imperfect, and should attempt to do it under the erroneous impression that they were perfect, he shows that this were even impossible to be done, though they wished it ever so much. For it would be necessary to seek another world. Wherefore he added, For you must needs then go out of the world. Do you see that he is no hard master, and that in his legislation he constantly regards not only what may be done, but also what may be easily done. For how is it possible, says he, for a man having care of a house and children, and engaged in the affairs of the city, or who is an artisan or a soldier, (the greater part of mankind being Greeks,) to avoid the unclean who are to be found every where? For by the fornicators of the world, he means those who are among the Greeks. But now I write unto you, If any brother be of this kind, with such an one no not to eat. Here also he glances at others who were living in wickedness.
But how can one that is a brother be an idolater? As was the case once in regard to the Samaritans who chose piety but by halves. And besides he is laying down his ground beforehand for the discourse concerning things offered in sacrifice to idols, which after this he intends to handle.
Or covetous. For with these also he enters into conflict. Wherefore he said also, Why not rather take wrong? Why not rather be defrauded? Nay, you yourselves do wrong and defraud.
Or a drunkard. For this also he lays to their charge further on; as when he says, One is hungry and another is drunken: and, meats for the belly and the belly for meats.
Or a reviler, or an extortioner: for these too he had rebuked before.
2. Next he adds also the reason why he forbids them not to mix with heathens of that character, implying that it is not only impossible, but also superfluous.