1 Corinthians 5:10

‘Not altogether with the fornicators of this world, or with the covetous and extortioners, or with idolaters. For then it would be necessary for you to go out of the world.'

He points out that he was not talking about dealings with non-Christians when he said avoid such people. Otherwise Christians would never have anything to do with any non-Christians, for they all disobey the commandments. Thus, while their ways must not be followed, and their sins must not be partaken of (Ephesians 5:7; 1 Timothy 5:22), Christians may have general dealings with them and befriend them. Judgment of them can be left to the judgment of God.

This does not necessarily mean that his teaching had not been clear. It may well be that he had expressed it clearly in a general sense but that it had been distorted by his critics who had wanted to bring him into disrepute, which they had done by deliberately misinterpreting what he had said.

Now he includes not just sexual immorality but also misbehaviour of any kind. If they were to avoid all immoral people, all greedy and ambitious people, all deceivers, cheats and blackmailers, and all idolaters, there would be no one left for them to keep company with in everyday life. And that would make life impossible. The only way to achieve it would be to leave the world altogether, and as slaves or employees many of them could not do that.