Transubstantiation is a doctrine or a core belief about the Eucharist. It is a technical theological term and a matter of faith that is often experienced as an intimidating concept, almost beyond comprehension, and difficult to explain. Yet, it is taught to our second graders at St. Bartholomew in preparation for their reception of first holy Communion, and once their sacramental preparation classes are completed, they are expected to be able to explain it to their parents.

This first task is to understand the word itself. “Transubstantiation” is derived from two Latin roots: “trans,” the prefix, which means “across” or “over,” and “substantia,” the root word, which means “substance.”

We ask the children, “What is a transatlantic flight?” They quickly reply, “An airplane flight across the Atlantic Ocean?” A person goes from one place to another. Then we ask, “What is a substance?” It is an abstract concept for a child, but the answer is “a thing” or “stuff,” or for those in STEM classes, a more advanced answer might be “physical matter.”

“Transubstantiation,” then, is to go across from one substance to another.

There are two initial substances with the Eucharist, bread and wine, and they cross over to two entirely new and different substances, the Body and Blood of Christ. It is no longer bread, but the Body of Christ under the appearance of bread; and it is no longer wine, but the Blood of Christ under the appearance of wine. The physical appearance and chemical composition remain unchanged, but the substance is entirely changed.

Next we ask, “Who first explained this?” “Jesus.” “When did he give his explanation?” “At the Last Supper?” “How did Jesus explain it?” Then we read the Gospel text: “Jesus took bread, said the blessing, broke it and … said, ‘Take and eat; this is my body’” (Mt 26:26).

The verb choice is intentional and crucial. Jesus said “is.” He did not say that the bread is a reminder, memento, symbol, a piece of bread that is especially spiritually important, or partly bread and partly body. Jesus said the bread is his Body. Jesus also said, “I am the living bread come down from heaven” (Jn 6:51). If Jesus says that the bread is changed into his Body, then we accept it as a matter of faith. Jesus spoke similarly regarding the wine: “This is my blood” (Mt 26:28).

As the lesson continues, another question is, “Who supplies the power that causes this change to take place?” The Eucharistic Prayer is offered by the priest in the name of Jesus, it is addressed to God the Father, and at the “epiclesis” — when the priest extends his hands over the bread and wine — the Holy Spirit is called upon “so that they may become for us the Body and Blood of our Lord Jesus Christ” (Eucharistic Prayer II). Thus, the power to change the bread and wine comes from all three Persons of the Most Holy Trinity.

The final question is, “When, and under what conditions, does transubstantiation take place?” It happens within a valid Catholic Mass with a properly ordained priest who is acting “in persona Christi,” in the person of Christ. The priest must be in union with the Church and in line with apostolic succession. Transubstantiation takes place at the moment of the consecration when the priest pronounces the words of institution: “This is my Body” and “This is the chalice of my Blood.” “The priest pronounces these words, but their power and grace are God’s,” said St. John Chrysostom, as quoted in the Catechism of the Catholic Church (No. 1375).

Father Van Sloun is pastor of St. Bartholomew in Wayzata. Read more of his writing at CatholicHotdish.com.