Transubstantiation

Jesus said to the Jewish crowds:

"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."

(Jn 6:51-58)