Why does Paul not tell Christians to avoid every immoral person in the world?
Paul limits separation to immoral people inside the church, not every immoral person in the world. Since the immoral, covetous, and wicked are the norm everywhere, avoiding all of them would require leaving the world entirely. Therefore believers are not told to withdraw from society's immoral people.
Les explains that Paul says when he tells believers not to have fellowship with immoral people, he is not talking about the immoral people out there in the workplace, but about those who are immoral and are members of your church. In verse 10, Paul writes, "Yet not altogether with the fornicators or the immoral people of this world, or with the covetous or the extortioners or with idolaters; because if you're not going to rub elbows with them, then you leave this world." The flip side is that if a man who is called a brother—claims to be a believer and is a member of the local congregation—is a fornicator, drunkard, or extortioner, the believer was not even to sit down and eat with such a person. This strong language had a purpose: to make that person feel set aside, no longer part of the Christian company, verboten, out of it, to bring him to his senses.
Yet not altogether with the fornicators of this world, or with the covetous, or extortioners, or with idolaters; for then must ye needs go out of the world.
More Questions
Did Paul mean Christians should completely avoid sinful people in the world?
Paul clarifies that he did not mean believers must avoid the fornicators, covetous, extortioners, and idolaters of this world altogether, because then they would have to go out of the world.
Who was Paul talking about when he said not to have fellowship with immoral people?
When Paul says not to fellowship with immoral people, he means immoral people who are members of your own church, not the immoral people out in the workplace or the world.