Mysterium Fidei
Christ Present in the Eucharist Through Transubstantiation
46To avoid any misunderstanding of this type of presence, which goes beyond the laws of nature and constitutes the greatest miracle of its kind, (50) we have to listen with docility to the voice of the teaching and praying Church. Her voice, which constantly echoes the voice of Christ, assures us that the way in which Christ becomes present in this Sacrament is through the conversion of the whole substance of the bread into His body and of the whole substance of the wine into His blood, a unique and truly wonderful conversion that the Catholic Church fittingly and properly calls transubstantiation. (51) As a result of transubstantiation, the species of bread and wine undoubtedly take on a new signification and a new finality, for they are no longer ordinary bread and wine but instead a sign of something sacred and a sign of spiritual food; but they take on this new signification, this new finality, precisely because they contain a new "reality" which we can rightly call ontological. For what now lies beneath the aforementioned species is not what was there before, but something completely different; and not just in the estimation of Church belief but in reality, since once the substance or nature of the bread and wine has been changed into the body and blood of Christ, nothing remains of the bread and the wine except for the species—beneath which Christ is present whole and entire in His physical "reality," corporeally present, although not in the manner in which bodies are in a place.
Writings of the Fathers
47This is why the Fathers felt they had a solemn duty to warn the faithful that, in reflecting upon this most sacred Sacrament, they should not pay attention to the senses, which report only the properties of bread and wine, but rather to the words of Christ, which have power great enough to change, transform, "transelementize" the bread and wine into His body and blood. As a matter of fact, as the same Fathers point out on more than one occasion, the power that does this is the same power of Almighty God that created the whole universe out of nothing at the beginning of time.
48"Instructed as you are in these matters," says St. Cyril of Jerusalem, at the end of a sermon on the mysteries of the faith, "and filled with an unshakeable faith that what seems to be bread is not bread—though it tastes like it—but rather the Body of Christ; and that what seems to be wine is not wine—even though it too tastes like it—but rather the Blood of Christ . . . draw strength from receiving this bread as spiritual food and your soul will rejoice." (52)
49St. John Chrysostom insists upon the same point with these words: "It is not man who makes what is put before him the Body and Blood of Christ, but Christ Himself who was crucified for us. The priest standing there in the place of Christ says these words, but their power and grace are from God. This is my Body, he says, and these words transform what lies before him." (53)
50Cyril, the Bishop of Alexandria, is in wonderful harmony with John, the Bishop of Constantinople, when he writes in his commentary on the Gospel of St. Matthew: "He said This is my body and this is my blood in a demonstrative fashion, so that you might not judge that what you see is a mere figure; instead the offerings are truly changed by the hidden power of God Almighty into Christ's body and blood, which bring us the life-giving and sanctifying power of Christ when we share in them." (54)
51Ambrose, the Bishop of Milan, in a clear statement on the Eucharistic conversion, has this to say: "Let us be assured that this is not what nature formed but what the blessing has consecrated; and there is greater power in the blessing than in nature, since nature itself is changed through the blessing." To confirm the truth of this mystery, he recounts many of the miracles described in the Sacred Scriptures, including Christ's birth of the Virgin Mary, and then he turns his mind to the work of creation, concluding this way: "Surely the word of Christ, who could make something that did not exist out of nothing, can change things that do exist into something they were not before. For it is no less extraordinary to give new natures to things than it is to change nature." (55)
Constant Teaching of the Popes and the Councils
52But this is no time for assembling a long list of evidence. Instead, We would rather recall the firmness of faith and complete unanimity that the Church displayed in opposing Berengarius who gave in to certain difficulties raised by human reasoning and first dared to deny the Eucharistic conversion. More than once she threatened to condemn him unless he retracted. Thus it was that Our predecessor, St. Gregory VII, commanded him to swear to the following oath: "I believe in my heart and openly profess that the bread and wine that are placed on the altar are, through the mystery of the sacred prayer and the words of the Redeemer, substantially changed into the true and proper and lifegiving flesh and blood of Jesus Christ our Lord, and that after the consecration they are the true body of Christ—which was born of the Virgin and which hung on the Cross as an offering for the salvation of the world—and the true blood of Christ—which flowed from His side—and not just as a sign and by reason of the power of the sacrament, but in the very truth and reality of their substance and in what is proper to their nature." (56)
53We have a wonderful example of the stability of the Catholic faith in the way in which these words meet with such complete agreement in the constant teaching of the Ecumenical Councils of the Lateran, Constance, Florence and Trent on the mystery of the Eucharistic conversion, whether it be contained in their explanations of the teaching of the Church or in their condemnations of error.
54After the Council of Trent, Our predecessor, Pius VI, issued a serious warning, on the occasion of the errors of the Synod of Pistoia, that parish priests not neglect to speak of transubstantiation, which is listed among the articles of the faith, in the course of carrying out their office of teaching. (57) Similarly, Our Predecessor of happy memory, Pius XII, recalled the bounds beyond which those who were carrying on subtle discussion of the mystery of transubstantiation might not pass; (58) and We Ourself, at the National Eucharistic Congress that was recently celebrated at Pisa, bore open and solemn witness to the faith of the Church, in fulfillment of Our apostolic duty. (59)
55Moreover, the Catholic Church has held firm to this belief in the presence of Christ's Body and Blood in the Eucharist not only in her teaching but in her life as well, since she has at all times paid this great Sacrament the worship known as "latria," which may be given to God alone. As St. Augustine says: "It was in His flesh that Christ walked among us and it is His flesh that He has given us to eat for our salvation; but no one eats of this flesh without having first adored it . . . and not only do we not sin in thus adoring it, but we would be sinning if we did not do so." (60)