It must be commanded by God. No creature has the right, or power to institute the worship of God. But good works (we speak of moral good) and the worship of God are the same. Moral good differs widely from natural good, inasmuch as all actions, in as far as they are actions, including even those of the wicked, are naturally good; but all actions are not morally good, or in accordance with the justice of God. This condition excludes all will-worship, as well as the figment of good intentions, as when men do evil that good may come, or when they perform works founded upon their own imaginations, which they endeavor to thrust upon God in the place of worship, which, indeed, are not evil in themselves, but yet are not commanded by God. It is not sufficient for the worship of God, that a work be not evil, or not prohibited: it must also be commanded by God, according to what the Scriptures declare, “To obey is better than sacrifice, and to hearken than the fat of rams.” “Walk in my statutes.” “In vain do they worship me, teaching for doctrines the commandments of men.” (1 Sam. 15:22. Ez. 20:19. Matt. 15:9.)
Zacharias Ursinus,, Commentary on the Heidelberg Catechism, trans. G. W. Williard (Cincinnati, OH: Elm Street Printing Company, 1888), 477.