"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." (John 6:53)
On hearing Jesus make this statement, many of his disciples said, "This is a hard teaching. Who can accept it?" and no longer followed him.
If we are Catholic or Orthodox we may not find this so hard because we believe it, or, at least, have grown so accustomed to hearing it that it does not strike us as a "scandal", i. e. a stumbling block. But it is clear that some followers of Jesus did, and also clear that he did not call them back to say that they had misunderstood, and he was only using an image or a figure of speech. They felt out of their depth. He let them go, because this was a basic and essential part of his teaching.
What did he mean by it? At this point we pass over from history (what happened, what Jesus said, etc.) to theology (how we are to understand our religion in the light of what happened or what was said).
At every Mass we attend, we hear the priest say in the Person of Christ himself, This is my body; this is my blood. Has something changed? The Church has always taught that on an ordinary physical level, the bread and wine remain the same: in appearance, colour, shape, taste. But what is on the altar is no longer simply bread and wine because it has been transformed into the real presence of the Risen Lord. They embody sacramentally the reality of the presence of Jesus and that fact does not allow us to consider this bread and wine simply as bread and wine.
It is clear from the Gospel that this was the belief of the Christians of John's community. Jesus told his hearers that the manna which their ancestors ate in the desert was not the food of immortality because all those who ate it died sooner or later. In the same way those whom he had fed with bread wished to make him their leader because he had given them bread. Really, however, he had come to give them better bread than that, just as he offered the Samaritan woman at the well better water than ordinary water. Manna might be called bread from heaven, but the true "bread of God is that which comes down from heaven, and gives life to the world." (John 6:27-34) Not only that, but God has given only one person authority to give this life-giving bread - the Son of man, Jesus himself.
The next step of the lesson is this: Jesus not only gives the bread of life; he is the bread of life. Those who come to him in faith do find only refreshment for their souls, but they will never die.
I am the living bread which came down from heaven; any one who eats of this bread will live for ever; and the bread which I shall give for the life of the world is my flesh. (John 6:51)
What does faith in Christ mean? It is just to agree that what he says is true and that you believe in it. It is to participate in his life. In the language Jesus spoke (Aramaic) "my flesh" could be another way of saying "myself": he himself is the bread for the life of the world.
What could he mean? Was he advocating cannibalism (which early Christians were accused of by the Roman authorities)? For the Jews, the drinking of any blood was offensive. Drinking the blood of a human being was a horrific idea.
Jesus answered by pointing out that his words were to be understood spiritually: It is the spirit that gives life, the flesh is to no avail. (John 6:63) But what was the spiritual meaning?
What we believe he meant was that those people who come in faith to Jesus and are united with him, have a share in his life, the life of God, which is eternal. To feed on Christ by faith is to eat the flesh of the Son of man and drink his blood and so have eternal life. Without faith our Holy Communion means nothing. With faith we are accepting God's invitation in Christ to share in God's life. This was very neatly expressed by a queen when asked her opinion of Christ's presence in the Sacrament:
'Twas God the Word that spake it,
He took the bread and brake it;
And what the Word did make it;
That I believe and take it.