1 Corinthians 5:10 - Ellicott's Commentary On The Whole Bible

Yet not altogether with the fornicators of this world. — This is a limitation and explanation of the command given not to associate with fornicators. It would have been almost impossible for the command to be literally obeyed without the Christian withdrawing altogether from the business of life, so the Apostle explains that it is the fair fame and purity of the Church which he is anxious to preserve. There are so many fornicators, and covetous, and idolaters in this world (i.e., the heathen world) that men must meet with them. But the Christian must tolerate no such sins among themselves; they must exclude from the social circle any brother who, bearing the name of Christ, indulges in the vices of the heathen world. The Church is to be the light of the world, and not the recipient of the world’s darkness.