This is an evidence that Paul was in constant trouble with some of his listeners about being an apostle. Not every one accepted him as an apostle. Hence the evidence that when he came from Damascus to Jerusalem to join the Apostles, perhaps to replace Judas who got lost and they said that Paul could not even be a disciple, let alone an apostle and Paul resented the rejection since he was an apostle to himself; self appointed one but still enough to put up his claim. (Acts 9:26)
I said
That's true Paul had his hecklers back then.