Reply Obj. 2: No creature can work miracles as the chief agent. Yet it can do so instrumentally, just as the touch of Christ's hand healed the leper. And in this fashion Christ's words change the bread into His body. But in Christ's conception, whereby His body was fashioned, it was impossible for anything derived from His body to have the instrumental power of forming that very body. Likewise in creation there was no term wherein the instrumental action of a creature could be received. Consequently there is no comparison.
Reply Obj. 3: The aforesaid words, which work the consecration, operate sacramentally. Consequently, the converting power latent under the forms of these sacraments follows the meaning, which is terminated in the uttering of the last word. And therefore the aforesaid words have this power in the last instant of their being uttered, taken in conjunction with those uttered before. And this power is simple by reason of the thing signified, although there be composition in the words uttered outwardly. _______________________
FIFTH ARTICLE [III, Q. 78, Art. 5]
Whether the Aforesaid Expressions Are True?
Objection 1: It seems that the aforesaid expressions are not true. Because when we say: "This is My body," the word "this" designates a substance. But according to what was said above (AA. 1, 4, ad 3; Q. 75, AA. 2, 7), when the pronoun "this" is spoken, the substance of the bread is still there, because the transubstantiation takes place in the last instant of pronouncing the words. But it is false to say: "Bread is Christ's body." Consequently this expression, "This is My body," is false.
Obj. 2: Further, the pronoun "this" appeals to the senses. But the sensible species in this sacrament are neither Christ's body nor even its accidents. Therefore this expression, "This is My body," cannot be true.
Obj. 3: Further, as was observed above (A. 4, ad 3), these words, by their signification, effect the change of the bread into the body of Christ. But an effective cause is understood as preceding its effect. Therefore the meaning of these words is understood as preceding the change of the bread into the body of Christ. But previous to the change this expression, "This is My body," is false. Therefore the expression is to be judged as false simply; and the same reason holds good of the other phrase: "This is the chalice of My blood," etc.
On the contrary, These words are pronounced in the person of Christ, Who says of Himself (John 14:6): "I am the truth."
I answer that, There have been many opinions on this point. Some have said that in this expression, "This is My body," the word "this" implies demonstration as conceived, and not as exercised, because the whole phrase is taken materially, since it is uttered by a way of narration: for the priest relates that Christ said: "This is My body."
But such a view cannot hold good, because then these words would not be applied to the corporeal matter present, and consequently the sacrament would not be valid: for Augustine says (Tract. lxxx in Joan.): "The word is added to the element, and this becomes a sacrament." Moreover this solution ignores entirely the difficulty which this question presents: for there is still the objection in regard to the first uttering of these words by Christ; since it is evident that then they were employed, not materially, but significatively. And therefore it must be said that even when spoken by the priest they are taken significatively, and not merely materially. Nor does it matter that the priest pronounces them by way of recital, as though they were spoken by Christ, because owing to Christ's infinite power, just as through contact with His flesh the regenerative power entered not only into the waters which came into contact with Christ, but into all waters throughout the whole world and during all future ages, so likewise from Christ's uttering these words they derived their consecrating power, by whatever priest they be uttered, as if Christ present were saying them.