Paul had visited the church in Corinth in ~56 AD, for the first time since founding it 6-7 years earlier.  During his visit, which he called his “painful visit”, Paul had been publicly humiliated by an individual in the church, who slandered Paul’s character and criticized him for failing to visit Corinth as he had planned.  Worse yet, the Corinthian believers for the most part had failed to support and defend Paul.  Hurt by these actions, Paul returned to Ephesus and wrote a strongly-worded letter to the church (this letter was lost; it is not in the Bible), exhorting them to discipline this individual, and repent of their failure to defend Paul.  This lost letter “grieved” the Corinthians, and Paul found himself at odds in his relationship with the church he had founded.  He wrote to them again (2nd Corinthians), and in today’s section (2 Corinthians 1:12 to 2:4), Paul defended his character and explained his actions.