What does Acts 19:18 mean?

When Paul arrives in Ephesus, he finds a strange mix of interactions with the supernatural. Some people are devout followers of John the Baptist's teaching that to follow God means to repent from sins and resolve to obey Him (Acts 19:1–7). Some are Jewish exorcists who use their religious traditions—and, later, the name of Jesus—to try to control demons (Acts 19:13–17). Others, however, practice witchcraft.

In response, Ephesus seems to be the only city where Paul extensively uses the Holy Spirit's authority to heal and expel demons (Acts 19:11–12). An interaction that leaves seven Jewish exorcists beaten and naked by the hand of a powerful demon makes the people of Ephesus realize Paul has real power. The magicians not only divulge their practices of witchcraft—thus emptying their spells of power—they burn their spell books (Acts 19:19).

This has a secondary effect on the culture that could be found in every Roman city: idol worship. Ephesus was the city of the temple to Artemis, and craftsmen earned a great deal of money by making and selling her idols. As people reject witchcraft and accept Christianity, they also reject Artemis worship. Seeing their livelihood threatened, the craftsmen guild nearly starts a riot. The town clerk settles them down, and Paul leaves quietly (Acts 19:21—20:1). But he writes the church in Ephesus a letter, further encouraging them to stand strong amidst spiritual warfare (Ephesians 6:12).