Paul’s ministry was effective, but the traveling Jewish exorcists (people who try to drive out evil spirits) had no real power. They used the name of Jesus as if it were a magic word. However, they did not have a personal relationship with him or the indwelling Holy Spirit (God’s Spirit living in believers).
This contrast shows the difference between true faith and empty practice (compare Matthew 12:27; Mark 9:38–39; Luke 9:49–50; 11:19).