1Corinthians 5:9-13 I wrote unto you in an epistle not to company with fornicators: Yet not altogether with the fornicators of this world, or with the covetous, or extortioners, or with idolaters; for then must you needs go out of the world. But now I have written unto you not to keep company, if any man that is called a brother be a fornicator, or covetous, or an idolater, or a railer, or a drunkard, or an extortioner; with such an one no not to eat. For what have I to do to judge them also that are without? do not you judge them that are within? But them that are without God judges. Therefore put away from among yourselves that wicked person.
‘I wrote unto you in an epistle not to company with fornicators.’ Either this present epistle or one that he had already written and not sent. Now, with a report of conditions in the congregation (1Cor. 16:17), he perhaps combined the first one with this epistle, enlarging upon the subject (1Cor. 5:9-11).
‘Yet not altogether with the fornicators of this world, or with the covetous, or extortioners, or with idolaters; for then must you needs go out of the world.’ Christians are not to leave the world. They must remain in it doing business with all kinds of sinners, but they are not to eat with a man claiming to be a Christian when he is a fornicator, a covetous man, an idolater, a railer, a drunkard, or an extortioner (1Cor. 5:9; 15:33).
‘For what have I to do to judge them also that are without? do not you judge them that are within?’ This judgement is required from all Christians to know others’ by their fruit as Christ commanded us to do in Matthew 7:16, 20. We are not to fellowship with unsaved individuals according to many Scriptures (1Cor. 5:9-13; 2Cor. 6:14 – 7:1; 2Jn. 1:10; Ps. 1:1). ‘Therefore put away from among yourselves that wicked person.’ Sixteen Biblical reasons for excommunication: Refusing to make peace (Mat. 18:15); causing divisions (Rom. 16:17); fornication (1Cor. 5:11-13); covetousness (1Cor. 5:11-13); idolatry (1Cor. 5:11-13); trouble making (1Cor. 5:11-13); drunkenness (1Cor. 5:11-13); extortion (1Cor. 5:11-13); refusal to love God (1Cor. 16:22); unbelief, infidelity (2Cor. 6:14); backsliding (2Cor. 13:1-2, 10); disorderly conduct (2Thess. 3:6); defying the truth (2Thess. 3:14); denying faith (1Tim. 1:19-20); false teaching (1Tim. 6:3-5; 2Jn. 1:10); being a heretic (Tit. 3:10-11).