Who was accusing Paul of being an imposter and a false teacher?
Paul faced accusations of being an imposter and false teacher from Judaizers out of Israel, from the pagan world, and even from believing Jews connected with the twelve in Jerusalem. They challenged his credentials because he lacked letters of commendation from Peter, though his ministry was proven by saved pagans.
Les explains that Paul was constantly being submarined by the Judaizers from Israel, by the pagan world, and even by believing Jews from the element of the twelve in Jerusalem, who accused him of being an imposter and a false teacher. Their charge was that he didn't have the credentials. If he could have had letters of commendation from Peter, he would not have had so many problems, but he didn't have that. All he had as proof of his ministry were the pagans who had been saved and set on the rock Christ Jesus. Les also notes this is in 2 Corinthians, written within about a year after the first letter, which had to correct horrible problems among the Corinthians, chiefly gross immorality.