Roman Catholic: “Why may not the kirk, for good causes, devise ceremonies to decor the sacraments, and others [of ] God’s service?”
Knox: “Because, the kirk ought to do nothing but in faith, and ought not to go before, but is bound to follow, the voice of the true Pastor.
It is not enough that man invents a ceremony and then gives it a signification, according to his pleasure. For so might the ceremonies of the Gentiles, and this day the ceremonies of Mohammed, be maintained. But if that anything proceeds from faith, it must have the word of God for the assurance. For you are not ignorant, that “faith comes by hearing, and hearing by the word of God.” [Rom. 10:17] Now, if you will prove that your ceremonies proceed from faith, and do please God, you must prove that God in expressed words has commanded them; or else you shall never prove that they proceed from faith, nor yet that they please God; but that they are sin, and do displease him, according to the words of the apostle, “Whatsoever is not of faith is sin.” [Rom. 14:23]
The question was not, nor is not, of meat or drink, whereunto the kingdom of God consists not; but the question is of God’s true worshipping, without the which we can have no society with God…. May we cast away what we please, and retain what we please? If it be well remembered, Moses, in the name of God, says to the people of Israel, “All that the Lord thy God commands thee to do, that do thou to the Lord thy God: Add nothing to it; diminish nothing from it.” By this rule, think I, the kirk of Christ will measure God’s religion, and not by that which seems good in their own eyes. [Cf. Deut. 12:32; 12:8.]
That God’s word damns your ceremonies, it is evident; for the plain and strait commandment of God is,“Not that thing which appears good in thy eyes shalt thou do to the Lord thy God, but what the Lord thy God has commanded thee; that do thou; add nothing to it; diminish nothing from it.” Now unless you are able to prove that God has commanded your ceremonies, this his former commandment will damn both you and them. [Cf. Deut. 4:2; 12:8, 32.]”
Selected Writings of John Knox (Dallas: Presbyterian Heritage Publications, 1995), 1:12-16.