Transubstantiation - Explanation

The complete change of the substance of bread and wine into the substance of Christ’s body and blood by a validly ordained priest during the consecration at Mass, so that only the accidents of bread and wine remain. The Apostles taught this from the beginning, but the term came later. The Eastern Fathers before the sixth century called it in Greek meta-ousiosis, “change of being.” The Western Church preferred the Latin transubstantiatio, “change of substance,” and inserted that term into the creed of the Fourth Lateran Council in 1215.

The Council of Trent, defining “the wonderful and singular conversion of the whole substance of the bread into the body, and the whole substance of the wine into the blood,” added, “which conversion the Catholic Church calls transubstantiation” (Denzinger 1652). After transubstantiation, the accidents of bread and wine do not inhere in any subject or substance whatever. Yet they are not make-believe; they are sustained in existence by divine power. CCC 2nd ed., p. 545

CCC 1373 Christ Jesus, who died, yes, who was raised from the dead, who is at the right hand of God, who indeed intercedes for us, is present in many ways to his Church: in his word, in his Church’s prayer, where two or three are gathered in my name, in the poor, the sick, and the imprisoned, in the sacraments of which he is the author, in the sacrifice of the Mass, and in the person of the minister. But he is present … most especially in the Eucharistic species.

CCC 1374 The mode of Christ’s presence under the Eucharistic species is unique. It raises the Eucharist above all the sacraments as the perfection of the spiritual life and the end to which all the sacraments tend. In the most blessed sacrament of the Eucharist the body and blood, together with the soul and divinity, of our Lord Jesus Christ and, therefore, the whole Christ is truly, really, and substantially contained.

This presence is called “real” – by which is not intended to exclude the other types of presence as if they could not be “real” too, but because it is presence in the fullest sense: that is to say, it is a substantial presence by which Christ, God and man, makes himself wholly and entirely present.

CCC 1375 It is by the conversion of the bread and wine into Christ’s body and blood that Christ becomes present in this sacrament. The Church Fathers strongly affirmed the faith of the Church in the efficacy of the Word of Christ and of the action of the Holy Spirit to bring about this conversion. Thus St. John Chrysostom declares:

It is not man that causes the things offered to become the Body and Blood of Christ, but he who was crucified for us, Christ himself. The priest, in the role of Christ, pronounces these words, but their power and grace are God’s. This is my body, he says. This word transforms the things offered.

And St. Ambrose says about this conversion:
Be convinced that this is not what nature has formed, but what the blessing has consecrated. The power of the blessing prevails over that of nature, because by the blessing nature itself is changed. . . . Could not Christ’s word, which can make from nothing what did not exist, change existing things into what they were not before? It is no less a feat to give things their original nature than to change their nature.

CCC 1376 The Council of Trent summarizes the Catholic faith by declaring: “Because Christ our Redeemer said that it was truly his body that he was offering under the species of bread, it has always been the conviction of the Church of God, and this holy Council now declares again, that by the consecration of the bread and wine there takes place a change of the whole substance of the bread into the substance of the body of Christ our Lord and of the whole substance of the wine into the substance of his blood. This change the holy Catholic Church has fittingly and properly called transubstantiation.”

CCC 1377 The Eucharistic presence of Christ begins at the moment of the consecration and endures as long as the Eucharistic species subsist. Christ is present whole and entire in each of the species and whole and entire in each of their parts, in such a way that the breaking of the bread does not divide Christ.

CCC 1378 Worship of the Eucharist. In the liturgy of the Mass we express our faith in the real presence of Christ under the species of bread and wine by, among other ways, genuflecting or bowing deeply as a sign of adoration of the Lord. The Catholic Church has always offered and still offers to the sacrament of the Eucharist the cult of adoration, not only during Mass, but also outside of it, reserving the consecrated hosts with the utmost care, exposing them to the solemn veneration of the faithful, and carrying them in procession.