Why did Paul have to correct the Corinthians in 1 Corinthians?
Paul had to correct the Corinthians in 1 Corinthians because that church was full of problems, and he had to address them. He almost felt bad about it. The context contrasts this with his later second letter, where his attitude shifted to encouragement and exhortation.
Les teaches that in 1 Corinthians Paul had to deal with a church full of problems and address them, and he almost felt bad about it. Then, within about a year, Paul writes a second letter with a whole different attitude: he is no longer condemning them but encouraging, exhorting, and boasting about them to the churches in Achaia and Macedonia, the two areas of Greece. That sets up his instructions in chapters 8 and 9 on Christian grace-age giving.