John 6:56-71:  [Jesus said,] “Those who eat my flesh and drink my blood abide in me, and I in them.  Just as the living Father sent me, and I live because of the Father, so whoever eats me will live because of me.  This is the bread that came down from heaven, not like that which your ancestors ate, and they died.  But the one who eats this bread will live forever.”  Jesus said these things while he was teaching in the synagogue at Capernaum.

When many of Jesus’s disciples heard it, they said, “This teaching is difficult; who can hear it?”  But Jesus, being aware that his disciples were complaining about it, said to them, “Does this offend you?  Then what if you were to see the Son of Man ascending to where he was before?  It is the spirit that gives life; the flesh is useless.  The words that I have spoken to you are spirit and life.  But among you there are some who do not believe.”  For Jesus knew from the first who were the ones that did not believe, and who was the one that would betray him.  And he said, “For this reason I have told you that no one can come to me unless it is granted by the Father.”

Because of this many of his disciples turned back and no longer went about with him.  So Jesus asked the twelve, “Do you also wish to go away?”  Simon Peter answered him, “Lord, to whom can we go?  You have the words of eternal life.  We have come to believe and know that you are the Holy One of God.” Jesus answered them, "Did I not choose you, the twelve?  Yet one of you is a devil."  Jesus was speaking of Judas son of Simon Iscariot, for Judas, though one of the twelve, was going to betray Jesus.