Catechism of the Council of Trent: The Holy Eucharist
Transubstantiation A Total Conversion
This conversion, then, is so effected that the whole substance of the bread is changed by the power of God into the whole substance of the body of Christ, and the whole substance of the wine into the whole substance of His blood, and this, without any change in our Lord Himself. He is neither begotten, nor changed, nor increased, but remains entire in His substance.
This sublime mystery St. Ambrose thus declares: You see how efficacious are the words of Christ. If the word of the Lord Jesus is so powerful as to summon into existence that which did not exist, namely the world, how much more powerful is His word to change into something else that which already has existence ?
Many other ancient and most authoritative Fathers have written to the same effect. We faithfully confess, says St. Augustine, that before consecration it is bread and wine, the product of nature; but after consecration it is the body and blood of Christ, consecrated by the blessing. The body, says Damascene, is truly united to the Divinity, that body which was derived from the virgin; not that the body thus derived descends from heaven, but that the bread and wine are changed into the body and blood of Christ.
This admirable change, as the Council of Trent teaches, the Holy Catholic Church most appropriately expresses by the word transubstantiation. Since natural changes are rightly called transformations, because they involve a change of form; so likewise our predecessors in the faith wisely and appropriately introduced the term transubstantiation, in order to signify that in the Sacrament of the Eucharist the whole substance of one thing passes into the whole substance of another.
According to the admonition so frequently repeated by the holy Fathers, the faithful are to be admonished against curious searching into the manner in which this change is effected. It defies the powers of conception; nor can we find any example of it in natural transmutations, or even in the very work of creation. That such a change takes place must be recognised by faith; how it takes place we must not curiously inquire.
No less of caution should be observed by pastors in explaining the mysterious manner in which the body of our Lord is contained whole and entire under the least particle of the bread. Indeed, discussions of this kind should scarcely ever be entered upon. Should Christian charity, however, require a departure from this rule, the pastor should remember first of all to prepare and fortify his hearers by reminding them that no word shall be impossible with God.
A Consequence Of Transubstantiation
The pastor should next teach that our Lord is not in the Sacrament as in a place. Place regards things only inasmuch as they have magnitude. Now we do not say that Christ is in the Sacrament inasmuch as He is great or small, terms which belong to quantity, but inasmuch as He is a substance. The substance of the bread is changed into the substance of Christ, not into magnitude or quantity; and substance, it will be acknowledged by all, is contained in a small as well as in a large space. The substance of air, for instance, and its entire nature must be present under a small as well as a large quantity, and likewise the entire nature of water must be present no less in a glass than in a river. Since, then, the body of our Lord succeeds to the substance of the bread, we must confess it to be in the Sacrament after the same manner as the substance of the bread was before consecration; whether the substance of the bread was present in greater or less quantity is a matter of entire indifference.
The Mystery of the Accidents without a Subject
We now come to the third great and wondrous effect of this Sacrament, namely, the existence of the species of bread and wine without a subject.
Proof From The Preceding Dogmas
What has been said in explanation of the two preceding points must facilitate for pastors the exposition of this truth. For, since we have already proved that the body and blood of our Lord are really and truly contained in the Sacrament, to the entire exclusion of the substance of the bread and wine, and since the accidents of bread and wine cannot inhere in the body and blood of Christ, it remains that, contrary to physical laws, they must subsist of themselves, inhering in no subject.
Proof From The Teaching Of The Church
This has been at all times the uniform doctrine of the Catholic Church; and it can be easily established by the same authorities which, as we have already proved, make it plain that the substance of the bread and wine ceases to exist in the Eucharist.
Advantages Of This Mystery
Nothing more becomes the piety of the faithful than, omitting all curious questionings, to revere and adore the majesty of this august Sacrament, and to recognise the wisdom of God in commanding that these holy mysteries should be administered under the species of bread and wine. For since it is most revolting to human nature to eat human flesh or drink human blood, therefore God in His infinite wisdom has established the administration of the body and blood of Christ under the forms of bread and wine, which are the ordinary and agreeable food of man.
There are two further advantages: first, it prevents the calumnious reproaches of the unbeliever, from which the eating of our Lord under His visible form could not easily be defended; secondly, the receiving Him under a form in which He is impervious to the senses avails much for increasing our faith. For faith, as the well known saying of St. Gregory declares, has no merit in those things which fall under the proof of reason.
The doctrines treated above should be explained with great caution, according to the capacity of the hearers and the necessities of the times.
The Effects of the Eucharist
But with regard to the admirable virtue and fruits of this Sacrament, there is no class of the faithful to whom a knowledge of them is not most necessary. For all that has been said at such length on this Sacrament has principally for its object, to make the faithful sensible of the advantages of the Eucharist. As, however, no language can convey an adequate idea of its utility and fruits, pastors must be content to treat of one or two points, in order to show what an abundance and profusion of all goods are contained in those sacred mysteries.
The Eucharist Contains Christ And Is The Food Of The Soul
This they will in some degree accomplish, if, having explained the efficacy and nature of all the Sacraments, they compare the Eucharist to a fountain, the other Sacraments to rivulets. For the Holy Eucharist is truly and necessarily to be called the fountain of all graces, containing, as it does, after an admirable manner, the fountain itself of celestial gifts and graces, and the author of all the Sacraments, Christ our Lord, from whom, as from its source, is derived whatever of goodness and perfection the other Sacraments possess. From this (comparison), therefore, we may easily infer what most ample gifts of divine grace are bestowed on us by this Sacrament.
It will also be useful to consider attentively the nature of bread and wine, which are the symbols of this Sacrament. For what bread and wine are to the body, the Eucharist is to the health and delight of the soul, but in a higher and better way. This Sacrament is not, like bread and wine, changed into our substance; but we are, in some wise, changed into its nature, so that we may well apply here the words of St. Augustine: I am the food of the grown. Grow and thou shalt eat Me; nor shalt thou change Me into thee, as thy bodily food, but thou shalt be changed into Me.
The Eucharist Gives Grace
If, then, grace and truth came by Jesus Christ, they must surely be poured into the soul which receives with purity and holiness Him who said of Himself: He that eateth my flesh and drinketh my blood abideth in me and I in him. Those who receive this Sacrament piously and fervently must, beyond all doubt, so receive the Son of God into their souls as to be ingrafted as living members on His body. For it is written: He that eateth me, the same also shall live by me; also: The bread which I will give is my flesh for the life of the world. Explaining this passage, St. Cyril says: The Word of God, uniting Himself to His own flesh, imparted to it a vivifying power: it became Him, therefore, to unite Himself to our bodies in a wonderful manner, through His sacred flesh and precious blood, which we receive in the bread and wine, consecrated by His vivifying benediction.
The Grace Of The Eucharist Sustains
When it is said that the Eucharist imparts grace, pastors must admonish that this does not mean that the state of grace is not required for a profitable reception of this Sacrament. For as natural food can be of no use to the dead, so in like manner the sacred mysteries can evidently be of no avail to a soul which lives not by the spirit. Hence this Sacrament has been instituted under the forms of bread and wine to signify that the object of its institution is not to recall the soul to life, but to preserve its life.
The reason, then, for saying that this Sacrament imparts grace, is that even the first grace, with which all should be clothed before they presume to approach the Holy Eucharist, lest they eat and drink judgment to themselves, is given to none unless they receive in wish and desire this very Sacrament. For the Eucharist is the end of all the Sacraments, and the symbol of unity and brotherhood in the Church, outside which none can attain grace.