John Calvin Commentary Acts 8:17

"Then laid they their hands on them, and they received the Holy Spirit." — Acts 8:17 (ASV)

When they had laid their hands. The laying on of hands follows prayers, by which they testify that the grace of the Spirit is not included in the external ceremony, which grace they humbly seek from God. And yet, when they confess that God is the author, they do not neglect the ceremony which was given to them by God for this purpose; and because they do not perform it rashly, the effect also accompanies it.

This is the benefit and efficacy of signs, because God works in them, and yet He remains the only giver of grace and distributes it according to His good pleasure; but let us remember that the laying on of hands was the instrument of God when He gave the visible graces of the Spirit to His people, and that since the Church has been deprived of such riches, it is now only an empty show without any substance.