John Gill Commentary Acts 8:11

"And they gave heed to him, because that of long time he had amazed them with his sorceries." — Acts 8:11 (ASV)

To him they had regard Which is repeated from the foregoing verse, for the sake of what follows:

because that of a long time he has bewitched them with sorceries; or because he had, it may be for many years, astonished them with his magic arts, and the pranks he played in the use of them.