What does Acts 19:34 mean?

A mob fighting for a cause is dangerous, but at least you can reason with them. A mob that doesn't know what they're protesting is more difficult to control.

The mob started as a marketing campaign. The silversmiths and other craftsmen who make idols and shrines of Greek gods realize the more Paul heals ailments, frees people from demons, and preaches about Jesus, the fewer people buy their idols. They are losing money and seek to remind the city of its loyalty to the goddess Artemis (Acts 19:23–27).

The city of Ephesus was extremely devoted to Artemis, and her temple is one of the Seven Wonders of the Ancient World. "Artemis" is just a name given to a local goddess, however. It was against Roman law to worship an unauthorized god, so communities used the names of Greek gods to continue worshiping their local gods. The Greek Artemis, also known to the Romans as Diana, was a hunter. The Ephesian version was the goddess of fertility and childbirth or the mother goddess, although she herself was a virgin.

To try to calm down the mob, the Jews send Alexander. It's unclear who Alexander is, but since he is not identified with Paul, he's probably a part of the local synagogue. The Jews may be concerned because the mob doesn't know the difference between Judaism and Christianity, and if they attack Paul they might go after the synagogue, as well. The crowd doesn't care about nuance, however. They know Alexander doesn't worship Artemis, so he can say nothing they want to hear (Acts 19:33).