Acts 19:34

‘But when they perceived that he was a Jew, all with one voice for about the space of two hours cried out, “Great is Artemis (Diana) of the Ephesians.” '

However, the sight of a Jew inflamed their feelings even more. They knew that the Jews too looked down on Artemis their goddess. So they shouted him down and for two hours chanted, ‘Great is Artemis of the Ephesians'. The whole matter had got totally out of hand (although the attention seems to some extent have turned away from Gaius and Aristarchus). After two hours the first fervour would have died down.

Luke may have mentioned this attempt by Alexander because it confirmed the uselessness of Paul's wish to enter the theatre and speak. He too was a Jew, and a monotheist, and as such he would have been given no more opportunity to speak than Alexander. Such people were clearly not welcome in the theatre at this time, whoever they were, Paul most of all. He could be sure from this that his presence would certainly not have done any good at all.