John Calvin Commentary Acts 8:7

"For [from] many of those that had unclean spirits, they came out, crying with a loud voice: and many that were palsied, and that were lame, were healed." — Acts 8:7 (ASV)

Unclean spirits. He briefly touches on certain kinds, so that we may know by what miracles they were led to attribute any authority to Philip. That crying with which the unclean spirits cried was a sign of resistance. Therefore, this greatly served to demonstrate the power of Christ, that He bound the devils with His commandment, though they resisted stubbornly.