Why did the Corinthians accuse Paul of not being a true apostle?
The Corinthians accused Paul of not being a true apostle because he lacked letters of commendation, had no recognized authority, and could not claim to have ministered with Christ for three years as Peter could. They compelled him to boast of his apostleship, though he should have been commended by them.
Les explains that the Corinthians constantly accused Paul of not being a rightful apostle. They said he had no authority and no letters of commendation. Unlike Peter, Paul could not say he had ministered with Christ for three years. So they compelled him to boast or claim his apostleship, even though he ought to have been commended by them. Paul had brought them out of paganism and into the light of the gospel of the grace of God, yet they turned against him and gave him no credit. He insisted he was in nothing behind the very chiefest apostles, though he claimed to be nothing himself; as an instrument of God, he was everything.