And since the conversion is expressed in this form as in being, it is necessary for the extremes of the conversion to be signified as they exist in the fact of conversion. But then the term whereunto has the proper nature of its own substance; whereas the term whence does not remain in its own substance, but only as to the accidents whereby it comes under the senses, and can be determined in relation to the senses. Hence the term whence of the conversion is conveniently expressed by the demonstrative pronoun, relative to the sensible accidents which continue; but the term whereunto is expressed by the noun signifying the nature of the thing which terminates the conversion, and this is Christ's entire body, and not merely His flesh; as was said above (Q. 76, A. 1, ad 2). Hence this form is most appropriate: "This is My body."
Reply Obj. 1: The ultimate effect of this conversion is not a becoming but a being, as stated above, and consequently prominence should be given to this in the form.
Reply Obj. 2: God's word operated in the creation of things, and it is the same which operates in this consecration, yet each in different fashion: because here it operates effectively and sacramentally, that is, in virtue of its signification. And consequently the last effect of the consecration must needs be signified in this sentence by a substantive verb of the indicative mood and present time. But in the creation of things it worked merely effectively, and such efficiency is due to the command of His wisdom; and therefore in the creation of things the Lord's word is expressed by a verb in the imperative mood, as in Gen. 1:3: "Let there be light, and light was made."
Reply Obj. 3: The term whence does not retain the nature of its substance in the being of the conversion, as the term whereunto does. Therefore there is no parallel.
Reply Obj. 4: The pronoun "My," which implicitly points to the chief person, i.e. the person of the speaker, sufficiently indicates Christ's person, in Whose person these words are uttered, as stated above (A. 1).
Reply Obj. 5: The conjunction "for" is set in this form according to the custom of the Roman Church, who derived it from Peter the Apostle; and this on account of the sequence with the words preceding: and therefore it is not part of the form, just as the words preceding the form are not. _______________________
THIRD ARTICLE [III, Q. 78, Art. 3]
Whether This Is the Proper Form for the Consecration of the Wine:
"This Is the Chalice of My Blood," Etc.?
Objection 1: It seems that this is not the proper form for the consecration of the wine. "This is the chalice of My blood, of the New and Eternal Testament, the Mystery of Faith, which shall be shed for you and for many unto the forgiveness of sins." For as the bread is changed by the power of consecration into Christ's body, so is the wine changed into Christ's blood, as is clear from what was said above (Q. 76, AA. 1, 2, 3). But in the form of the consecration of the bread, the body of Christ is expressly mentioned, without any addition. Therefore in this form the blood of Christ is improperly expressed in the oblique case, and the chalice in the nominative, when it is said: "This is the chalice of My blood."
Obj. 2: Further, the words spoken in the consecration of the bread are not more efficacious than those spoken in the consecration of the wine, since both are Christ's words. But directly the words are spoken—"This is My body," there is perfect consecration of the bread. Therefore, directly these other words are uttered—"This is the chalice of My blood," there is perfect consecration of the blood; and so the words which follow do not appeal to be of the substance of the form, especially since they refer to the properties of this sacrament.