What does Acts 19:12 mean?
Paul's ministry doesn't often include healing miracles or exorcisms. In Philippi, Paul didn't expel the fortune-telling demon from the slave girl until it had irritated him over the course of several days (Acts 16:16–18). When the apostles started the church in Jerusalem, they healed quite a bit; apparently even Peter's shadow healed people (Acts 5:14–16; 8:7). Paul, however, typically uses words, showing how Jesus is the Messiah promised in the Jewish Scriptures. He isn't described as healing again until after being shipwrecked on his way to Rome (Acts 28:8).But Paul is in Ephesus, a city so well known for witchcraft that the phrase "Ephesian writings" means magical spells. In the synagogue, Paul shows Jews and Gentile God-fearers how relying on the Mosaic law for salvation doesn't work: they need to redirect their faith to Jesus. In the city, Paul does the same with magicians. Demon-empowered magic only enslaves. Jesus frees and heals.
The resistance Paul finds because of his healing ministry in Ephesus parallels his experience in Philippi. In Philippi, the owners of the possessed slave girl had Paul arrested because they could no longer make money from her fortune-telling (Acts 16:19–24). In Ephesus, so many people abandon their witchcraft and Artemis worship that the silversmiths who make shrines fear for their livelihoods (Acts 19:18–19, 23–27). It's interesting to consider how often people reject Jesus' offer of salvation not because they don't believe it's real but because it would cost them money.
In the Gospels, some people were healed by touching Jesus' robes (Matthew 9:20–22; 14:34–36). This does not validate the modern practice of "prayer cloths." Some prayer cloths are just reminders that one's friends are praying for them. Many times, however, televangelists sell pieces of cloth they claim have the power to heal, earn money, or otherwise send God's blessings. They are often sold by prosperity gospel preachers to take more money from their victims. Praying over a friend while you knit her a blanket is a warm and loving thing to do. Demanding money for a magical piece of fabric is for frauds.