God may be wrongly worshiped either by false worship or by superfluous worship being paid Him. . . . The ceremonies and practices of the Jewish religion signified that the Messiah was to come, and so now, after the coming of Our Lord, they could not be employed without superstition [=false worship]. Inasmuch as falsehood in religion is a grave injury to God, this species of superstition is mortally sinful.

(Fr. Thomas Slater, S.J., A Manual of Moral Theology, vol. 1, 3rd ed. [Benziger Brothers, 1908], pp. 215-216; bold print added for emphasis.)