In the 1902 encyclical letter of Pope Leo XIII, Mirae Caritatis, the Holy Father writes the following striking words:
[The Holy Eucharist] is, as it were, the very soul of the Church [velut anima Ecclesiae], and to it the grace of the priesthood is ordered and directed in all its fullness and through the various degrees of order. From the same source, the Church draws and has all her strength, all her glory, her every supernatural endowment and adornment, every good thing that is here; wherefore she makes it the greatest of all her cares to prepare and lead the hearts of the faithful to an intimate union with Christ through the Sacrament of His Body and Blood, and to draw them thereto.
These words form the basis of an expression often heard in the Church's modern catechesis today, namely, that the Eucharist is the "source and summit" of the entire Christian life (see Lumen Gentium, 11 and the Catechism of the Catholic Church, 1324). The above quotation from Pope Leo XIII explains the foundational reason why this is the case: the Holy Eucharist is the height of every spiritual gift and blessing because the Blessed Sacrament is the very soul of the Catholic Church — it is what animates the Church and gives her life, as Pope John Paul II wrote in his 2023 Holy Thursday encyclical letter, Ecclesia de Eucharistia Vivit (The Church lives from the Holy Eucharist).
The Holy Eucharist can be called the heart and soul of the Catholic Church because it embodies a profound mystery that transcends mere ritual; it represents the very essence of the Christian religion. To understand why the Eucharistic Mystery is regarded as the soul of the Church, one must explore its theological significance, its role in the life of the believing Catholic, and its profound impact on the community of Faith.
At the core of our Catholic religion is the belief that the Blessed Sacrament does not just contain grace (as do all the Sacraments), but rather that it contains the very Author and Source of all grace: Our Lord Jesus Christ Himself. Holy Mother Church teaches that through the words of Consecration that the Priest says at every Mass in persona Christi (that is, in the very Person of Christ Himself), the substances of bread and wine are transformed into the actual Body and Blood of Christ through a process known as transubstantiation. This means the entire substance (substantia) of bread and of wine are changed (trans) into Our Lord's Body and Blood, His human soul, and His Divinity. The Flesh and Blood of Christ are of His physical human nature; His soul is from His spiritual human nature; and to both are added His Divine Nature as the Second Person of the Most Holy Trinity.
While the substance of bread and of wine are changed at the Consecration at Holy Mass, the accidents (which is a philosophical term referring to the qualities or attributes) of the bread and wine remain unchanged. Thus, though we are communicating with the Body of Christ, it does not taste like human flesh but rather like ordinary bread. But the change that occurs is no less real.
The Blessed Sacrament is not simply a symbol that represents the Lord Jesus Christ. It is rather a true and real sacrificial offering that makes present upon the Altar Christ's Passion and Death. As such, the Eucharistic Mystery is at the core of the Christian religion. Without the Holy Eucharist, there is no Christianity.
The Holy Eucharist serves as spiritual nourishment for Catholics by allowing them to enter into an ever deeper communion with God. Just as physical food sustains the human body, the Angelic Food of the Blessed Sacrament strengthens and builds up the soul, helping it to enter into a more profound relationship with Christ.
Moreover, the Real Presence of Christ in the Blessed Sacrament is an affirmation of our hope of Eternal Life. It is, according to the Church's beautiful Eucharistic hymns, a "pledge of future glory." When we Catholics partake of this Divine Sacrament, we are not only celebrating Christ's Presence among us, but also anticipating the fulfillment of the promise of that Presence for all eternity. While containing, properly speaking, the Crucified and Suffering Lord, this Sacrament also gives powerful witness to His glorious Resurrection — and with that, His victory over sin and eternal death.
A soul is what animates a body. It is what gives life to what would otherwise be a lifeless body. A human body without a soul is simply a corpse. Aristotelian realist philosophy teaches that all reality is a composite of matter and form. Matter refers to the "building blocks" of something that exists. It answers the question, "What is it made of?" Form, on the other hand, gives matter a specific determination or orientation. Form is what makes a thing what it is and not something else.
What makes a human being a human being? It is not his body. Contrary to what modern science claims, a man is not human simply because of his material body, his DNA, etc: he is human because of his soul. Modern science does not grasp this truth, for the simple reason that what we call "science" today is materialistic in nature. Even the contemporary "science" of psychology tries to understand the human mind and how human beings think and behave with no reference whatsoever to the soul. And yet the soul is not just the principle of life that animates an otherwise dead body: it is also the defining characteristic of what it means to be human. We are human because we have a human soul. This, by the way, is why there is a difference between the Angels in Heaven (which are pure spirits) and the Saints in Heaven who do not yet have their resurrected bodies united to them. Saints are the souls of men and so, contrary to a popular myth today, we cannot say that when we die we "become Angels." Man is not a pure spirit; his soul in Heaven (until the resurrection of the body takes place at the end of time) is simply a soul that is no longer united to its body for a period of time. A pure spirit, on the other hand (i.e. an Angel) does not have a body at all as a part of its nature.
We can use this idea that it is the soul that makes man what he is (namely, a human being) in an analogical way and ask the question, "What is the soul of the Church?" The Church is, after all, the Mystical Body of Christ, and as such she possesses a certain person-ality. The Church is a mystical person, which is what the expression Mystical Body of Christ means. As a consequence, she possesses certain characteristics similar to those possessed by a human person. What is it then, in the Church, that animates the Church, that gives her Divine Life, that makes her what she truly is: the Mystical Body of Jesus Christ Our Lord?
We return to the encyclical of Pope John Paul II, Ecclesia de Eucharistia : the Church lives from the Holy Eucharist. And to Pope Leo XIII's Mirae Caritatis : the Blessed Sacrament is the very soul of the Church. All the Church's spiritual life flows from the Sacrament that is made present upon our Catholic Altars at every Catholic Mass. Without it, the Church would die; she would cease to exist. The great saints, like St. Pius of Pietrelcina ("Padre Pio") understood this truth very well. It was he who famously said, "The earth could exist more easily without the sun than could the Church without the Holy Sacrifice of the Mass."
This same sentiment was echoed by Pope Benedict XVI at the Mass of Corpus Christi in Rome in June 2011:
Without the Holy Eucharist, the Church simply does not exist.
The Catholic Mass, as a Sacrifice and as the Real Presence, is indeed the soul that animates the Church and makes her the Mystical Body of Our Lord. And this is why every attack against Christ is expressed as an attack against the Catholic Church, and particularly as an attack against the Blessed Sacrament (or the Priesthood, because without validly ordained Priests, there would be no Holy Eucharist). The enemy knows well that the Holy Eucharist is the soul of the Church, and therefore the Catholic Church's greatest and most powerful treasure, a treasure without which the faithful could not survive.
But do Catholics know and live of this sublime truth as well?
Know, O Christian, that the Mass is the holiest act of religion. You cannot do anything to glorify God more, nor profit your soul more, than by devoutly assisting at it, and assisting as often as possible. -St. Peter Julian Eymard