Objection 1. It would seem that there cannot be anything pernicious in the worship of the true God. It is written (Joel 2:32): "Everyone that shall call upon the name of the Lord shall be saved." Now whoever worships God calls upon His name. Therefore all worship of God is conducive to salvation, and consequently none is pernicious.
Objection 2. Further, it is the same God that is worshiped by the just in any age of the world. Now before the giving of the Law the just worshiped God in whatever manner they pleased, without committing mortal sin: wherefore Jacob bound himself by his own vow to a special kind of worship, as related in Genesis 28. Therefore now also no worship of God is pernicious.
Objection 3. Further, nothing pernicious is tolerated in the Church. Yet the Church tolerates various rites of divine worship: wherefore Gregory, replying to Augustine, bishop of the English (Regist. xi, ep. 64), who stated that there existed in the churches various customs in the celebration of Mass, wrote: "I wish you to choose carefully whatever you find likely to be most pleasing to God, whether in the Roman territory, or in the land of the Gauls, or in any part of the Church." Therefore no way of worshiping God is pernicious.
On the contrary, Augustine [Jerome (Ep. lxxv, ad Aug.) See Opp. August. Ep. lxxxii] in a letter to Jerome (and the words are quoted in a gloss on Galatians 2:14) says that "after the Gospel truth had been preached the legal observances became deadly," and yet these observances belonged to the worship of God. Therefore there can be something deadly in the divine worship.
I answer that, As Augustine states (Cont. Mendac. xiv), "a most pernicious lie is that which is uttered in matters pertaining to Christian religion." Now it is a lie if one signify outwardly that which is contrary to the truth. But just as a thing is signified by word, so it is by deed: and it is in this signification by deed that the outward worship of religion consists, as shown above (Question 81, Article 07). Consequently, if anything false is signified by outward worship, this worship will be pernicious.
Now this happens in two ways. On the first place, it happens on the part of the thing signified, through the worship signifying something discordant therefrom: and in this way, at the time of the New Law, the mysteries of Christ being already accomplished, it is pernicious to make use of the ceremonies of the Old Law whereby the mysteries of Christ were foreshadowed as things to come: just as it would be pernicious for anyone to declare that Christ has yet to suffer. On the second place, falsehood in outward worship occurs on the part of the worshiper, and especially in common worship which is offered by ministers impersonating the whole Church. For even as he would be guilty of falsehood who would, in the name of another person, proffer things that are not committed to him, so too does a man incur the guilt of falsehood who, on the part of the Church, gives worship to God contrary to the manner established by the Church or divine authority, and according to ecclesiastical custom. Hence Ambrose [Comment. in 1 ad Cor. 11:27, quoted in the gloss of Peter Lombard] says: "He is unworthy who celebrates the mystery otherwise than Christ delivered it." For this reason, too, a gloss on Colossians 2:23 says that superstition is "the use of human observances under the name of religion."
Reply to Objection 1. Since God is truth, to invoke God is to worship Him in spirit and truth, according to John 4:23. Hence a worship that contains falsehood, is inconsistent with a salutary calling upon God.
Reply to Objection 2. Before the time of the Law the just were instructed by an inward instinct as to the way of worshiping God, and others followed them. But afterwards men were instructed by outward precepts about this matter, and it is wicked to disobey them.
Reply to Objection 3. The various customs of the Church in the divine worship are in no way contrary to the truth: wherefore we must observe them, and to disregard them is unlawful.
Source: Summa Theologica (New Advent)