"To respond to this invitation we must prepare ourselves for so great and so holy a moment. St. Paul urges us to examine our conscience: 'Whoever, therefore, eats of the bread or drinks the cup of the Lord in an unworthy manner will be guilty of profaning the body and blood of the Lord. Let a man examine himself, and so eat of the bread and drink of the cup. For anyone who eats and drinks without discerning the body eats and drinks judgment upon himself' (1 Cor 11: 27-29). Anyone conscious of a grave sin must receive the sacrament of reconciliation before coming to communion" (Catechism of the Catholic Church, 1385).
Scripture Text: (1 COR 11:23-26)
Brothers and sisters:
I received from the Lord what I also handed on to you,
that the Lord Jesus, on the night he was handed over,
took bread, and, after he had given thanks,
broke it and said, "This is my body that is for you.
Do this in remembrance of me."
In the same way also the cup, after supper, saying,
"This cup is the new covenant in my blood.
Do this, as often as you drink it, in remembrance of me."
For as often as you eat this bread and drink the cup,
you proclaim the death of the Lord until he comes.
Transubstantiation means "change of substance", or "change of reality." When the priest repeats the words that Jesus spoke at the Last Supper, the bread is no longer bread, and the wine is no longer wine. Instead, the entire substance of the bread and the entire substance of the wine have been changed into the substance of The Body and Blood of Christ.
Transubstantiation occurs only by the power of God, and in a way that we cannot empirically detect. We know that transubstantiation takes place through the certainty of faith.
Dr. Scott Hahn, the famous former Protestant minister that converted to Catholicism wrote in his conversion story one of the most beautiful testimonies about the Eucharist that I have ever read. Here are his words, written in his book that he co-authored with his wife Kimberly.
"Then one day, I made a 'fatal blunder' - I decided that it was time for me to go to Mass on my own. Finally I resolved to darken the doors of Gesu, Marquette University's parish. Right before noon, I slipped quietly into the basement chapel for daily Mass. I wasn't sure what to expect; maybe I'd be alone with a priest and a couple of old nuns. I took a seat as an observer in the back pew. All of a sudden lots of ordinary people began coming in off the streets; rank-and-file type folks. They came in, genuflected, knelt and prayed. Their simple but sincere devotion was impressive. Then a bell rang and a priest walked out toward the altar. I remained seated; I still wasn't sure if it was safe to kneel. As an evangelical Calvinist, I had been taught that the Catholic Mass was the greatest sacrilege that a man could commit – “to re-sacrifice Christ” - so I wasn't sure what to do. I watched and listened as the readings, prayers and responses - so steeped in Scripture - made the Bible come alive. I almost wanted to stop the Mass and say, 'Wait. That line is from Isaiah; the song is from the Psalms. Whoa, you've got another prophet in that prayer'. I found numerous elements from the ancient Jewish liturgy that I had studied so intensely. All of a sudden I realized, this is where the Bible belongs. This was the setting in which this precious family heirloom was meant to be read, proclaimed and expounded. Then we moved into the Liturgy of the Eucharist, where all my covenant conclusions converged. I wanted to stop everything and shout, 'Hey, can I explain what's happening from Scripture? This is great!' Instead I just sat there, famished with a supernatural hunger for the Bread of Life. After pronouncing the words of consecration, the priest held up the Host. I felt as if the last drop of doubt had drained from me. With all of my heart, I whispered, 'My Lord and my God. That's really you! And if that's you, then I want full communion with you. I don't want to hold anything back' (Rome Sweet Home, pp. 87-88).
Today, the Feast of Corpus Christi reminds us that we possess an immense treasure. When a Catholic priest takes a little piece of unleavened bread and repeats the words that Jesus spoke at the Last Supper, "This is my body", and when he takes a small of amount of wine in a chalice and says, "This is my blood", the bread is no longer bread and the wine is no longer wine.
At every Holy Sacrifice of the Mass, we participate in a marvelous miracle!