Every year, during the Third Week of Easter, we have readings at daily Mass from the 6th chapter of John's Gospel. This chapter is essential for understanding what the Catholic Church teaches about the Eucharistic Presence of Jesus.
At the Last Supper, Jesus said: "This is my body" (see Matthew 26: 26; Mark 14: 22; Luke 22: 19; 1 Corinthians 11: 24). Was Jesus speaking symbolically or literally? Not everything Jesus said was meant to be taken literally.
For example, in the Sermon on the Mount, Jesus said: "If your right eye causes you to sin, tear it out and throw it away. ... If your right hand causes you to sin, cut it off and throw it away" (Matthew 5: 29-30). Jesus did not want to be taken literally here. He was using hyperbole to get across the point that hell exists and that we should avoid anything that leads to alienation from God. The crowd knew he was not speaking literally because at the end of his teaching no one stopped following him. I imagine that if anyone in the crowd had taken Jesus literally, that person would have left, saying "I'll be back in about 20 or 30 years!"
However the reaction is very different when it comes to Jesus' teaching in John 6. It begins with Jesus talking about how God gave bread from heaven (manna) to the Israelites in the desert and that everyone who listens to the Father will come to Jesus. He says, "I am the bread of life" (6: 35, 48). Some people have interpreted this to mean that the teaching of Jesus nourishes, that his words should be chewed or reflected upon. But Jesus makes it clear that he is not speaking symbolically when he says "the bread that I will give is my flesh for the life of the world" (6: 51). At this point an argument breaks out: "How can this man give us his flesh to eat?" (6: 52). Jesus could have clarified the matter for them, telling them not to take him so literally, but he doesn't. He hammers home the point by saying "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" (6: 53). Clearly, Jesus is speaking literally.
What's interesting is that those who have trouble accepting Jesus' teaching are not the crowd nor his enemies but his followers. We read: "Then many of his disciples who were listening said, 'This saying is hard; who can accept it?'" (6: 60). And, "As a result of this, many of his disciples returned to their former way of life and no longer accompanied him" (6: 66).
If he were speaking symbolically or with hyperbole, as he was in the Sermon on the Mount, he would have stopped them from walking away. But he didn't. He meant his words to be taken literally. This is the mystery of the Eucharist. Bread and wine become the Body and Blood of Christ because he said so. And the 6th chapter of John's Gospel confirms that he was speaking literally and not figuratively.