“This is my body”
For I received from the Lord that which also I delivered to you, that the Lord Jesus on the night in which he was betrayed took bread. When he had given thanks, he broke it, and said, “Take, eat. This is my body, which is broken for you. Do this in memory of me.” In the same way he also took the cup, after supper, saying, “This cup is the new covenant in my blood. Do this, as often as you drink, in memory of me.” For as often as you eat this bread and drink this cup, you proclaim the Lord’s death until he comes. Therefore whoever eats this bread or drinks the Lord’s cup in a way unworthy of the Lord will be guilty of the body and the blood of the Lord. But let a man examine himself, and so let him eat of the bread, and drink of the cup. For he who eats and drinks in an unworthy way eats and drinks judgment to himself, if he doesn’t discern the Lord’s body.
1 Corinthians 11:23-29In context. Paul to the Corinthians, correcting a Supper where the rich ate before the poor: he hands on the words of institution, ‘do this in memory of me’, and warns that eating unworthily is to be guilty of the body and blood of the Lord.
One more passage: John 6:60-69
Therefore many of his disciples, when they heard this, said, “This is a hard saying! Who can listen to it?” But Jesus knowing in himself that his disciples murmured at this, said to them, “Does this cause you to stumble? Then what if you would see the Son of Man ascending to where he was before? It is the spirit who gives life. The flesh profits nothing. The words that I speak to you are spirit, and are life. But there are some of you who don’t believe.” For Jesus knew from the beginning who they were who didn’t believe, and who it was who would betray him. He said, “For this cause I have said to you that no one can come to me, unless it is given to him by my Father.” At this, many of his disciples went back, and walked no more with him. Jesus said therefore to the twelve, “You don’t also want to go away, do you?” Simon Peter answered him, “Lord, to whom would we go? You have the words of eternal life. We have come to believe and know that you are the Christ, the Son of the living God.”
John 6:60-69In context. The same scene, after the hard words: many disciples leave. Jesus says the Spirit gives life and ‘the flesh profits nothing’, and Peter answers for the Twelve that they will stay.
Scripture’s words can be read more than one way. Paul treats the Supper as a real sharing in Christ, and warns that eating unworthily is guilt; he also keeps calling it bread. How Christ is present can be read more than one way.
The Catholic reading
Jesus took bread and said “this is my body”, not “this represents”. Paul says to eat unworthily is to be guilty of his body and blood. Ignatius, a generation after John, and Justin, Irenaeus and Cyril after him, call the bread the flesh of Christ; no father taught a bare memorial.
“a conversion is made of the whole substance of the bread into the substance of the body of Christ our Lord”
Council of Trent, Session 13, chapter 4, 1551
The Protestant reading
Jesus also said “I am the door” and “I am the vine”, and at the table his body sat in front of them, unbroken. Paul still calls it bread after the blessing. The fathers also spoke of sign and figure (Augustine), and transubstantiation was defined in 1215. Lutherans take “is” literally without it; the Reformed take it as a sign that gives what it signifies.
“Transubstantiation (or the change of the substance of Bread and Wine) in the Supper of the Lord, cannot be proved by holy Writ”
Thirty-nine Articles, Article 28, 1571