What immorality problem in 1 Corinthians grieved the apostle Paul?
The problem was gross immorality in the church, dealt with in 1 Corinthians 5. A believer had stooped to such a low level that it grieved the apostle, and the church was not addressing it. Paul addressed it in his first letter, and later it was apparently corrected.
Les explains that the four groups in Corinth caused dissension and grief to the apostle and were part of their carnality; they simply did not grow spiritually. The Corinthians had sent the apostle a letter with a long list of questions about how they were handling various problems, and among those problems was the situation in chapter 5. There was gross immorality, and it grieved the apostle that a believer would stoop to such a low level while the church was not addressing it. Paul dealt with this in the first letter. Later, when writing 2 Corinthians, Paul seems to indicate that many of these things were now corrected, since his first letter did not fall on deaf ears; enough time had elapsed that they could clean up their act.
More Questions
Was there opposition in the Corinthian church to disciplining the immoral man?
There was a minority in the church who opposed the discipline, like liberals today who say to leave the man alone because people are people.
Which chapter of 1 Corinthians is Paul referring to in 2 Corinthians when he mentions the wrongdoer?
The individual Paul refers to in 2 Corinthians is the man of 1 Corinthians 5, the chapter Paul deals with most, since Paul uses the pronoun 'his,' showing he means one man, an individual.