Council of Trent: Session 13
Chapter 2
On the reason of the Institution of this most holy Sacrament.
Wherefore, our Saviour, when about to depart out of this world to the Father, instituted this Sacrament, in which He poured forth as it were the riches of His divine love towards man, making a remembrance of his wonderful works; and He commanded us, in the participation thereof, to venerate His memory, and to show forth his death until He come to judge the world. And He would also that this sacrament should be received as the spiritual food of souls, whereby may be fed and strengthened those who live with His life who said, He that eateth me, the same also shall live by me; and as an antidote, whereby we may be freed from daily faults, and be preserved from mortal sins. He would, furthermore, have it be a pledge of our glory to come, and everlasting happiness, and thus be a symbol of that one body whereof He is the head, and to which He would fain have us as members be united by the closest bond of faith, hope, and charity, that we might all speak the same things, and there might be no schisms amongst us.
Chapter 3
On the excellency of the most holy Eucharist over the rest of the Sacraments.
The most holy Eucharist has indeed this in common with the rest of the sacraments, that it is a symbol of a sacred thing, and is a visible form of an invisible grace; but there is found in the Eucharist this excellent and peculiar thing, that the other sacraments have then first the power of sanctifying when one uses them, whereas in the Eucharist, before being used, there is the Author Himself of sanctity. For the apostles had not as yet received the Eucharist from the hand of the Lord, when nevertheless Himself affirmed with truth that to be His own body which He presented (to them). And this faith has ever been in the Church of God, that, immediately after the consecration, the veritable Body of our Lord, and His veritable Blood, together with His soul and divinity, are under the species of bread and wine; but the Body indeed under the species of bread, and the Blood under the species of wine, by the force of the words; but the body itself under the species of wine, and the blood under the species of bread, and the soul under both, by the force of that natural connexion and concomitancy whereby the parts of Christ our Lord, who hath now risen from the dead, to die no more, are united together; and the divinity, furthermore, on account of the admirable hypostatical union thereof with His body and soul. Wherefore it is most true, that as much is contained under either species as under both; for Christ whole and entire is under the species of bread, and under any part whatsoever of that species; likewise the whole (Christ) is under the species of wine, and under the parts thereof.