Roger Nutt, General Principles of Sacramental Theology (Washington, DC: Catholic University of America Press, 2017), 62-63.

Several clarifications merge from Thomas's definition of the sacraments that distinguish the seven from other symbolic gestures employed by the Church. First, the sacraments are not efficacious merely as moral realities. Morally efficacious realities may be conducive to bringing about a certain state of affairs, but they do not “make” the state of affairs. Stop signs, for example, are extremely efficacious in bringing automobiles to a halt, but there is nothing about them that is intrinsic to making cars stop. Stop signs are efficacious because they are good reminders. As a stand-alone category, therefore, moral efficacy is not sufficient to articulate the relation between the sacraments and the conferral of holiness upon their recipients. 

Second, and related to the previous point,  the sacraments are not simply dispositions to grace. Thomas considers  the use of certain sacred signs that dispose things for sanctifying actions, such as the blessing of a religious item with holy water or the consecration of an altar. The sign, in these cases, disposes or sets apart the blessed item or consecrated altar for sacred purposes. Thomas the eyes that sacraments operate this way in relation to Holiness and the conferral of grace. Sacraments do not merely dispose their recipients to grace, they actually make them holy. “Things that signify disposition to holiness,” Thomas explains, “are not called sacraments . . . only those things are called sacraments which signify the perfection of holiness in man” [ST III, q. 60, a. 2, ad 3]. This is so, Thomas explains, because a “disposition is not an end, whereas a perfection is” [ibid.]. A disposition is ordered to something else, but the sacraments effect the end of perfection or holiness in men or women.

Third, the sacraments employ natural realities (e.g., water, wine, oil, bread) but they are not natural signs. The sacraments have a divine origin and corresponding purpose or intention for their employment. Thomas is very sensitive to the nuances of Christian anthropology, and his common dictum that “the thing known is in the knower according to the mode of the knower” [ST I, q. 12, a. 4] is certainly applicable to sacramental theology. But the sacraments do not complement Christian anthropology as if they were emanations from human nature. Rather, they complement human nature because God, in his wisdom, knows the best way to lead humanity to himself. “Signs are given to men,” Thomas explains, “to whom it is proper to discover the unknown by means of the known” [ST III, q. 60, a. 2].

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