The Catholic Church teaches that the bread actually changes into the Flesh of the risen Christ by the words of institution spoken in the person of Christ by the priest. Likewise, by the power of Christ's one priesthood, exercised through ordained priests, the wine changes into the Blood of the risen Christ. This is what’s called transubstantiation — one substance changing into another substance.
There are examples of transubstantiation in the Bible. The Book of Exodus recounts how Aaron, as commanded by Moses, turned the Nile river into blood. Similarly, the Gospel of John relates how Jesus turned water into wine at the wedding feast of Cana.
On "The Download—The Eucharist," Christine Niles reveals that Pope St. John Paul the Second commissioned Fr. John Hardon, S.J. to teach the faithful specifically about how Christ is made actually and completely present by the Blessed Sacrament.
Father Hardon employs the word "concomitance" when teaching about the Real Presence as did St. Thomas Aquinas 800 years earlier. Concomitance means a relationship of distinct things that are inseparably together. Such examples are a living body with its soul and the three Divine Persons in the Trinity.
In teaching about transubstantiation, during the first consecration of bread and the second consecration of the wine, Fr. Hardon affirms:
But only the substance of his body is the specific effect of the first consecration at Mass; his blood, soul, divinity, and personality become present by concomitance, i.e., by the inseparable connection that they have with his body. In the second consecration, the conversion terminates specifically in the presence of the substance of Christ's blood. But again by concomitance his body and entire self become present as well.
By the power of Christ's priesthood, at the utterance of the efficacious words "This is My Body," the bread changes solely into the resurrected and glorified Flesh of Christ. But wherever the Body of the risen Christ becomes present by transubstantiation, the Blood, Soul and Divinity of the resurrected Christ becomes becomes truly present by concomitance, as they cannot be separated in the one living Christ.
The "Download" panel discussed some of the various heresies pertaining to the Eucharist: consubstantiation, transfinalization and transignification. All of these errors have one thing in common—they deny that the consecrated bread changes into the actual Flesh of the crucified and risen Christ.
These errors occur because human eyes, beholding Jesus, are deceived by the false appearances of bread and wine. Jesus is the Eucharist; but His bodily presence is masked by the mere appearances of the bread and wine, which aren't actually there.
Think of the burning bush that Moses saw on Mt. Horeb in the Book of Exodus, which had the appearance of being on fire but was not consumed. Think too of the many angels that appeared as if they had an actual human body, which they don't. As Raphael told Tobias, "I seemed indeed to eat and to drink with you," but didn't in reality.
Jesus changed His appearance at times in the Gospel. One instance was on the road to Emmaus, as St. Mark recounts: "He appeared in another shape to two of them walking." And as St. Luke records, "Jesus himself also drawing near, went with them. But their eyes were held, that they should not know him."
Jesus is still appearing in the Flesh today as the Eucharist, but we can only recognize him with the eyes of faith.
Watch the full episode: "The Download—The Eucharist."