The celebration of this sacrament is called a sacrifice for two
reasons. First, because, as Augustine says (Ad Simplician. ii), "the images of
things are called by the names of the things whereof they are the images; as
when we look upon a picture or a fresco, we say, 'This is Cicero and that is
Sallust.'" But, as was said above (79, 1), the celebration of this sacrament
is an image representing Christ's Passion, which is His true sacrifice.
Accordingly the celebration of this sacrament is called Christ's sacrifice.
Hence it is that Ambrose, in commenting on Heb. 10:1, says: "In Christ was
offered up a sacrifice capable of giving eternal salvation; what then do we do?
Do we not offer it up every day in memory of His death?" Secondly it is called
a sacrifice, in respect of the effect of His Passion: because, to wit, by this
sacrament, we are made partakers of the fruit of our Lord's Passion . . .
Summa Theologica III qu. 83, art. 1.
[Objection 2. Further, Christ's sacrifice
was made upon the cross, whereon "He delivered Himself for us, an oblation and
a sacrifice to God for an odor of sweetness," as is said in Eph. 5:2. But
Christ is not crucified in the celebration of this mystery. Therefore, neither
is He sacrificed.] Reply to Objection 2. As the
celebration of this sacrament is an image representing Christ's Passion, so the
altar is representative of the cross itself, upon which Christ was sacrificed
in His proper species. Summa Theologica III qu. 83, art. 1, ad
2.
[Objection 3. Further, as Augustine says
(De Trin. iv), in Christ's sacrifice the priest and the victim are one and the
same. But in the celebration of this sacrament the priest and the victim are
not the same. Therefore, the celebration of this sacrament is not a sacrifice
of Christ.] Reply to Objection 3. For the same
reason (cf. Reply to Obj. 2) the priest also bears Christ's image, in Whose
person and by Whose power he pronounces the words of consecration, as is
evident from what was said above (82, 1,3). And so, in a measure, the priest
and victim are one and the same. Summa Theologica III qu. 83, art. 1,
ad 3.