I have also no difficulty in conceding to you that there is nothing more perilous to our salvation than a distorted and perverse worship of God. The primary rudiments by which we are wont to train to piety those whom we wish to win as disciples to Christ, are these: not to frame any new worship of God for themselves at random and their own pleasure, but to know that the only legitimate worship is that which he himself approved from the beginning. For we maintain, what the sacred oracle declared, that obedience is more excellent than any sacrifice (1 Sam. 15:22). In short, we train them by every means to keep within the one rule of worship which they have received from his mouth, and bid farewell to all fictitious worship.
—Calvin’s Reply To Sadoleto (1539) in J. K. S. Reid ed., Calvin: Theological Treatises (Louisville, KY; London: Westminster John Knox Press, 1954), 229.