As to the effect, considered in each of the partakers. For, as Ambrose (Mag. Sent. iv, D, xi) says on 1 Cor. 11:20, this sacrament "avails for the defense of soul and body"; and therefore "Christ's body is offered" under the species of bread "for the health of the body, and the blood" under the [...]
"In relation to Christ's Passion, in which the blood was separated from the body. And therefore in this sacrament, which is the memorial of our Lord's Passion, the bread is received apart as the sacrament of the body, and the wine as the sacrament of the blood." -St. Thomas Aquinas
"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.' As to the second because it was immolated by the entire multitude of the children of Israel on the fourteenth day [...]
"Because last words, chiefly such as are spoken by departing friends, are committed most deeply to memory; since then especially affection for friends is more enkindled, and the things which affect us most are impressed the deepest in the soul. Consequently, since, as Pope Alexander I says, 'among sacrifices there can be none greater than [...]
"It was necessary accordingly that there should be at all times among men something to show forth our Lord's Passion; the chief sacrament of which in the old Law was the Paschal Lamb. Hence the Apostle says (1 Cor. 5:7): 'Christ our Pasch is sacrificed.' But its successor under the New Testament is the sacrament [...]
"This sacrament has a threefold significance. one with regard to the past, inasmuch as it is commemorative of our Lord's Passion, which was a true sacrifice, as stated above (Q[48], A[3]), and in this respect it is called a 'Sacrifice.' With regard to the present it has another meaning, namely, that of Ecclesiastical unity, in [...]
"The reality of the sacrament is the unity of the mystical body, without which there can be no salvation; for there is no entering into salvation outside the Church, just as in the time of the deluge there was none outside the Ark, which denotes the Church." -St.Thomas Aquinas
"The reality of the sacrament can be had through the very desire of receiving the sacrament. Before actual reception of this sacrament, a man can obtain salvation through the desire of receiving it, just as he can before Baptism through the desire of Baptism… Spiritual food changes man into itself, according to that saying of [...]
"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 [...]
"The Apostle says (1 Cor. 10:17): 'For we, being many, are one bread, one body, all that partake of one bread': from which it is clear that the Eucharist is the sacrament of the Church's unity. But a sacrament bears the likeness of the reality whereof it is the sacrament. Therefore the Eucharist is one [...]