The Doctrine of Transubstantiation: Is Jesus Really Present in the Eucharist?

Jesus first repeated what he said, then summarized: "‘I am the living bread which came down from heaven; if any one eats of this bread, he will live for ever; and the bread which I shall give for the life of the world is my flesh.’ The Jews then disputed among themselves, saying, ‘How can this man give us his flesh to eat?’" (John 6:51–52).

His listeners were stupefied because now they understood Jesus literally—and correctly. He again repeated his words, but with even greater emphasis, and introduced the statement about drinking his blood: "Truly, truly, I say to you, unless you eat the flesh of the Son of man and drink his blood, you have no life in you; he who eats my flesh and drinks my blood has eternal life, and I will raise him up at the last day. For my flesh is food indeed, and my blood is drink indeed. He who eats my flesh and drinks my blood abides in me, and I in him" (John 6:53–56).

Notice that Jesus made no attempt to soften what he said, no attempt to correct "misunderstandings," for there were none. Our Lord’s listeners understood him perfectly well. They no longer thought he was speaking metaphorically. If they had, if they mistook what he said, why no correction?

On other occasions when there was confusion, Christ explained just what he meant (cf. Matt. 16:5–12). Here, where any misunderstanding would be fatal, there was no effort by Jesus to correct. Instead, he repeated himself for greater emphasis.

~ Catholic Answers; excerpt from Christ in the Eucharist ~