Thomas Aquinas

“ A thing is one in perfection, when it is complete through the presence of all that is needed for its end; as a man is complete by having all the members required for the operation of his soul, and a house by having all the parts needful for dwelling therein. And so this sacrament is said to be one. Because it is ordained for spiritual refreshment, which is conformed to corporeal refreshment. ”

“ Another difference is because by Baptism a man is ordained to the Eucharist, and therefore from the fact of children being baptized, they are destined by the Church to the Eucharist; and just as they believe through the Church's faith, so they desire the Eucharist through the Church's intention, and, as a result, receive its reality. But they are not disposed for Baptism by any previous sacrament, and consequently before receiving Baptism, in no way have they Baptism in desire ”

“ No one should entertain the slightest doubt, that then every one of the faithful becomes a partaker of the body and blood of Christ, when in Baptism he is made a member of Christ's body; nor is he deprived of his share in that body and chalice even though he depart from this world in the unity of Christ's body, before he eats that bread and drinks of that chalice. ”

“ Now it is clear that just as generation is required for corporeal life, since thereby man receives life; and growth, whereby man is brought to maturity: so likewise food is required for the preservation of life. ”

“ In relation to Christ crucified, Who is contained in this sacrament, its figures were all the sacrifices of the Old Testament, especially the sacrifice of expiation, which was the most solemn of all. While with regard to its effect, the chief figure was the Manna, "having in it the sweetness of every taste" (Wis. 16:20) , just as the grace of this sacrament refreshes the soul in all respects.
The Paschal Lamb foreshadowed this sacrament in these three ways. First of all, because it was eaten with unleavened loaves, according to Ex. 12:8: "They shall eat flesh . . . and unleavened bread." ”

“ Consequently the Eucharist is not one sacrament but several.
Objection 2: Further, it is impossible for genera to be multiplied without the species being multiplied: thus it is impossible for one man to be many animals. But, as stated above ( [4511] Q [60] , A [1] ) , sign is the genus of sacrament. Since, then, there are more signs than one, to wit, bread and wine, it seems to follow that here must be more sacraments than one.
Objection 3: Further, this sacrament is perfected in the consecration of the matter, as stated above (A [1] , ad 3) . ”