Note 6 at Acts 19:12: The power of God is spiritual in nature but it can be manifest physically. This happened with Jesus when virtue or power physically flowed out of him and healed people (Lk. 6:19). The robe of Jesus became a conductor of the power of God between Jesus and the woman who touched the hem of his garment (Mt. 9:20-22; Mk. 5:25-34; and Lk. 8:43-48). This is the same principle that's involved in the laying on of hands (see note 17 at Mk. 16:18, p. 566).

Paul simply applied this principle by faith to such a degree that he transferred the anointing of God to handkerchiefs and aprons and then when these materials came in contact with sick or demon possessed people, they were delivered. Although it is not specifically stated, it is understood that the people who received the benefit had to exercise some degree of faith to make this work just as it was with Jesus (see note 2 at Mk. 6:5, p. 219). To have effect on others without their consent is not God's way. That is like magic and is in the realm of witchcraft.