In demanding miracles of us, they act dishonestly. For we are not forging some new gospel, but are retaining that very gospel whose truth all the miracles that Jesus Christ and his disciples ever wrought serve to confirm. But, compared with us, they have a strange power: even to this day they can confirm their faith by continual miracles!
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Perhaps this false hue could have been more dazzling if Scripture had not warned us concerning the legitimate purpose and use of miracles. For Mark teaches that those signs which attended the apostles’ preaching were set forth to confirm it [Mark 16:20]. In like manner, Luke relates that our ‘Lord . . . bore witness to the word of his grace,’ when these signs and wonders were done by the apostles’ hands [Acts 14:3 p.]. Very much like this is that word of the apostle: that the salvation proclaimed by the gospel has been confirmed in the fact that ‘the Lord has attested it by signs and wonders and various mighty works [Heb. 2:4 p.; cf. Rom 15:18-19]
John Calvin, “Prefatory Address to King Francis,” in The Institutes of the Christian Religion, ed. John T. McNeill, trans. Ford Lewis Battles, (Philadelphia: Westminster, 1960), 16.
It seems from what Calvin says here that he believed that miracles were given during the giving of revelation as a sign of its authenticity. It also seems that he believed there to be no more need for signs after the revelation had been first given.