John Calvin on Acts 8:17

17. When they had laid their hands. The laying on of hands followeth prayers, whereby they testify that the grace of the Spirit is not included in the external ceremony, which they crave humbly at the hands of another. And yet when they confess that God is the author, they neglect not the ceremony which was delivered them by God to this use; and because they usurp it not rashly, the effect is also annexed. This is the profit and efficacy of signs, because God worketh in them, and yet he remaineth the only giver of grace and distributeth the same according to his good pleasure; but let us remember that the laying on of hands was the instrument of God, at such time as he gave the visible graces of the Spirit to his, and that since the Church was deprived of such riches, it is only a vain visor without any substance. “Inane duntaxat esset spectrum,” it was only an empty specter.

Acts 8:18-25

18. And when Simon saw that the Holy Ghost was given by the laying on of the apostles' hands, he offered them money, 19. Saying, Give me also this power, that on whom I shall lay my hands, he may receive the Holy Ghost. 20. And Peter said unto him, Thy money perish with thee, because thou hast thought that the gift of God is obtained with money. 21. Thou hast no part nor inheritance in this business; for thy heart is not right before God. 22. Therefore repent of this wickedness, and pray unto God, if peradventure the cogitation of thy heart may be forgiven thee. 23. For I see that thou art in the gall of bitterness, and in the bond of unrighteousness. 24. And Simon answering, said, Pray ye for me unto God, that none of these things may happen to me which ye have said. 25. Then when they had testified and spoken the word of God, they returned to Jerusalem, and they preached the gospel in many streets of the Samaritans.