Today is the Feast of Corpus Christi in the Catholic church. In Latin ‘corpus’ means body and ‘Christi’ means Christ. In Greek it is written as Κόρπους Κρίστι. The Lord himself instituted the consumption of His body and blood at the last supper, the first Catholic Mass. Read Christ’s bread of life discourse. These are the words of Jesus himself. “’I am the bread of life. Your ancestors ate the manna in the desert, but they died; this is the bread that comes down from heaven so that one may eat it and not die. I am the living bread that came down from heaven; whoever eats this bread will live forever; and the bread that I will give is my flesh for the life of the world.’ The Jews quarreled among themselves, saying, ‘How can this man give us [his] flesh to eat?’ Jesus said to them, ‘Amen, amen, I say to you, unless you eat the flesh of the Son of Man and drink his blood, you do not have life within you. Whoever eats my flesh and drinks my blood has eternal life, and I will raise him on the last day. For my flesh is true food, and my blood is true drink. Whoever eats my flesh and drinks my blood remains in me and I in him. Just as the living Father sent me and I have life because of the Father, so also the one who feeds on me will have life because of me. This is the bread that came down from heaven. Unlike your ancestors who ate and still died, whoever eats this bread will live forever.’ These things he said while teaching in the synagogue in Capernaum.” Gospel of John, Chapter 6, verses 48-59. Paul wrote about it in 1 Corinthians 10:16-17. “The cup of blessing that we bless, is it not a participation in the blood of Christ? The bread that we break, is it not a participation in the body of Christ? Because the loaf of bread is one, we, though many, are one body, for we all partake of the one loaf.”
At all gatherings of the followers of Christ since His death in 33 A.D. until the Protestant Reformation in 1517 A.D., they presented wine and bread to the faithful. The Mass was celebrated in house churches for the first 300 years for fear of Roman persecution, especially if they worshipped the Lord openly in public. Many suffered martyrdom. They were an underground Church until the year 312 A.D. when Roman Emperor Constantine was converted to Christianity by God himself. The following words are a description of a Mass entitled The Constitution of James, the Brother of John, the Son of Zebedee believed to have been written about the year 400 A.D. It is found in the Apostolic Constitutions (Book VIII) at the following site: https://www.newadvent.org/fathers/07158.htm
“[W]e offer to You, our King and our God, according to His constitution, this bread and this cup, giving You thanks, through Him, that You have thought us worthy to stand before You, and to sacrifice to You; and we beseech You that You will mercifully look down upon these gifts which are here set before You, O God, who standest in need of none of our offerings. And accept them, to the honour of Your Christ, and send down upon this sacrifice Your Holy Spirit, the Witness of the Lord Jesus' sufferings, that He may show this bread to be the body of Your Christ, and the cup to be the blood of Your Christ, that those who are partakers thereof may be strengthened for piety, may obtain the remission of their sins, may be delivered from the devil and his deceit, may be filled with the Holy Ghost, may be made worthy of Your Christ, and may obtain eternal life upon Your reconciliation to them, O Lord Almighty.”
If these words do not reflect a belief in transubstantiation, then no words other than Jesus’ will convince you that bishops and priests, since the death of Christ, have the power through the Holy Spirit to change bread and wine into the body and blood of Christ. In transubstantiation the whole substance of the bread and wine is changed into the body and blood of Christ, only the outward appearance of bread and wine remains. The converted bread and wine is called the Eucharist. I know many of you do not believe in transubstantiation, even many Catholics. Most Protestants make fun of the Catholics for such beliefs, yet they will pass around crackers and grape fruit juice in their services.
“In 1263 a German priest, Fr. Peter of Prague, made a pilgrimage to Rome. He stopped in Bolsena, Italy, to celebrate Mass at the Church of St. Christina. At the time he was having doubts about Jesus being truly present in the Blessed Sacrament. He was affected by the growing debate among certain theologians who, for the first time in the history of the Church, began introducing doubts about the Body and Blood of Christ being actually present in the consecrated bread and wine. In response to his doubt, when he recited the prayer of consecration as he celebrated the Holy Sacrifice of the Mass, blood started seeping from the consecrated host and onto the altar and corporal. Fr. Peter reported this miracle to Pope Urban IV, who at the time was nearby in Orvieto. The pope sent delegates to investigate and ordered that host and blood-stained corporal be brought to Orvieto. The relics were then placed in the Cathedral of Orvieto, where they remain today.
This Eucharistic Miracle confirmed the visions given to St. Juliana of Mont Cornillon in Belgium (1193-1258). St. Juliana was a nun and mystic who had a series of visions in which she was instructed by Our Lord to work to establish a liturgical feast for the Holy Eucharist, to which she had a great devotion. After many years of trying, she finally convinced the bishop, the future Pope Urban IV, to create this special feast in honor of the Blessed Sacrament, where none had existed before. Soon after her death, Pope Urban instituted Corpus Christi for the Universal Church and celebrated it for the first time in Orvieto in 1264, a year after the Eucharistic Miracle in Bolsena.” https://www.catholiccompany.com/magazine/feast-of-corpus-christi-story-6077