John Calvin on Acts 8:9

9. A certain man named Simon. This was such a let that it might seem that the gospel could have no passage to come unto the Samaritans; for the minds of them all were bewitched with Simon’s jugglings. And this amazedness was grown to some strength by reason of long space of time. Furthermore experience teacheth what a hard matter it is to pluck that error out of the minds of men which hath taken root through long continuance and to call them back unto a sound and right mind who are already hardened. Superstition made them more obstinate in their error, because they counted Simon not only as a prophet of God, but even as the Spirit of God.