© Copyright 2003 Grace D. MacKinnon

This article taken from the book Dear Grace: Answers to Questions About the Faith, coming in March 2003 from Our Sunday Visitor. Order online by e-mail at or call 1-800-348-2440. Faith questions may be sent to Grace via e-mail at: You may also visit Grace online at

Let us say at the onset that the answer is going to seem very mysterious. But, then again, many truths of the Christian faith are bewildering and appear to be inexplicable. Among these, the Eucharist is indeed a unique “mystery of faith.” Yet, we have the words of Jesus, who said clearly, “This is my body, which is given for you; do this in remembrance of me” (Luke 22:19, see also Matthew 26:26, Mark 14:22). So, the Church was left with trying to understand and explain this mystery. She had no choice because the Lord Himself had said it. If we had been at the Last Supper, would we have questioned Him?

The Church, from the beginning, accepted and believed in the Real Presence. At the Council of Trent, this belief was officially articulated by stating that, at the consecration of the bread and wine, a change takes place in which the entire substance of the bread is changed into the substance of the Body of Christ our Lord, and the entire substance of the wine into the substance of His Blood. This change the Holy Catholic Church fittingly and properly calls “transubstantiation” (Session 13, n. 4).

What do we mean by transubstantiation? Here we must turn to philosophy. It was by applying the philosophy of Aristotle that St. Thomas Aquinas was able to explain the change that takes place in the Sacred Host at Mass. We notice that the Church’s statement only speaks of the “substance” of the bread and wine. This is precisely what we want to understand. What do we mean in saying that only the “substance” changes? This, by the way, is what the word transubstantiation means — “a change in substance.”

When one looks out at the created world and observes anything — whether it is a person, animal, or object — there are only two ways to perceive it: (1) through the senses and (2) through the mind. In other words, everything in nature is more than what it “appears” to be. It has an outward appearance and an inner nature. To keep it simple, let us take, for example, a tree. There are many kinds of trees in various shapes, colors and sizes, but every time we point to one — no matter what kind it is — we say “tree.” This is because, regardless of what each particular tree may look like on the outside, they all share in the same nature or essence of being a tree.

This inner nature or essence is what philosophy calls “substance” and the outward qualities or attributes of its appearance (its color, shape, size, or smell) are called “accidents.” We perceive its “accidents” through our senses because we see it with our eyes, we feel it by touch, and we smell it also. But its “substance,” we perceive through our mind because we “know” from our experience what a tree is supposed to be.

Now, let us say we have two trees, one real and one artificial. In appearance the two are identical, but one is “real” with the underlying reality being wood; the other is a tree only in appearance with the underlying reality being plastic. What we say in regard to the Eucharist is that just as we can affirm God's power to change a plastic tree into a real tree or a real tree into a plastic tree, without altering the outside appearance (accidents), then we should be able to make the leap of faith and affirm that God can change bread and wine into the Body and Blood of Christ without altering the accidents (appearance, taste, touch) of bread and wine. After all, we do acknowledge God's power to create something from nothing (as with the creation of the entire universe). If that is the case, then we should have no difficulty affirming God’s power to use one created thing to make another. Does he do this with the Eucharist? Jesus' words supply the proof: “This is my body … This is my blood…”

But how does this apply to what happens to the bread and wine offered at Mass? For the Mass to be a true sacrifice, we must have three elements: (1) a priest, (2) a victim, and (3) an altar. At the Mass, the priest stands in the Person of Christ (in Persona Christi) and thus Jesus is the true priest (as He was at the Last Supper) and what He offers is Himself — He is both priest and victim. The table is the altar. When the priest says the words of consecration, the whole substance (or essence) of the bread changes into the substance of the body of Christ, while the accidents, (the taste, texture, color) of the bread remain as they were before. In other words, He is there in essence but not in appearance — the bread and wine will still look, smell, and taste like bread and wine. We perceive Him, not through our senses, but through our mind — we “know” He is there because He said it: “This is my body.”

It is not by the power of man that the bread and wine become the Body and Blood of Christ, but by the power of the Holy Spirit. Can He do this? He most certainly can, and He does. He is God.

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