What does 1 Corinthians 4:18 mean?

Paul's letter is full of hard words for the Christians in Corinth. He wants them to change their attitudes and behavior in several significant ways. Now he writes that he knows some among them who will refuse to change because they don't expect Paul to show up in person. Paul has noted his role as the Corinthians' spiritual "father" (1 Corinthians 4:15). This is a very "fatherly" statement: to point out that someone is only likely to obey when they think their "father" is going to catch them in the act.

He describes these people as arrogant, bold in their defiance of Paul because of the distance between them. Paul will assure them in the following verse that he does plan to come to them in person.

Why would Paul being among them make a difference? The Corinthians will remember that Paul's preaching was backed up by demonstrations of the supernatural power of the Holy Spirit (1 Corinthians 2:1–5). He does not expect that these prideful resisters of his correction will put up much of a fight when they are looking him in the eye. Even in the ancient era, humanity showed its tendency to "talk tough" and put on a brave face, so long as they didn't have to meet those they claimed to stand against.