11 God did powerful things through Paul, things quite out of the ordinary. 12 The word got around and people started taking pieces of clothing - handkerchiefs and scarves and the like - that had touched Paul's skin and then touching the sick with them. The touch did it - they were healed and whole.
13 Some itinerant Jewish exorcists who happened to be in town at the time tried their hand at what they assumed to be Paul's "game." They pronounced the name of the Master Jesus over victims of evil spirits, saying, "I command you by the Jesus preached by Paul!" 14 The seven sons of a certain Sceva, a Jewish high priest, were trying to do this on a man 15 when the evil spirit talked back: "I know Jesus and I've heard of Paul, but who are you?"
Matthew Henry's Commentary on Acts 19:11-15
Commentary on Acts 19:8-12
(Read Acts 19:8-12)
When arguments and persuasions only harden men in unbelief and blasphemy, we must separate ourselves and others from such unholy company. God was pleased to confirm the teaching of these holy men of old, that if their hearers believed them not, they might believe the works.
Commentary on Acts 19:13-20
(Read Acts 19:13-20)
It was common, especially among the Jews, for persons to profess or to try to cast out evil spirits. If we resist the devil by faith in Christ, he will flee from us; but if we think to resist him by the using of Christ's name, or his works, as a spell or charm, Satan will prevail against us. Where there is true sorrow for sin, there will be free confession of sin to God in every prayer and to man whom we have offended, when the case requires it. Surely if the word of God prevailed among us, many lewd, infidel, and wicked books would be burned by their possessors. Will not these Ephesian converts rise up in judgement against professors, who traffic in such works for the sake of gain, or allow themselves to possess them? If we desire to be in earnest in the great work of salvation, every pursuit and enjoyment must be given up which hinders the effect of the gospel upon the mind, or loosens its hold upon the heart.