In the Gospel of John, Jesus is recorded as speaking;
"I am the living Bread which came down from Heaven. If any man eat of this Bread, he shall live for ever; and the Bread that I will give is My flesh, which I will give for the life of the world.” John 6:51
What did Jesus mean?
John 6:51 I am the living bread that came down from heaven. If anyone eats of this bread, he will live forever. And the bread that I will give for the life of the world is my flesh.”
52 The Jews then disputed among themselves, saying, “How can this man give us his flesh to eat?” 53 So Jesus said to them, “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.
Jesus, speaking about this to His disciples said the following:
John 6:60 When many of his disciples heard it, they said, “This is a hard saying; who can listen to it?” 61 But Jesus, knowing in himself that his disciples were grumbling about this, said to them, “Do you take offense at this? 62 Then what if you were to see the Son of Man ascending to where he was before?
63 It is the Spirit who gives life; the flesh is no help at all. The words that I have spoken to you are spirit and life.
Jesus is called the Word of God in John (John 1:1-3, John 1:14)
The way I understand what Jesus said about eating His flesh and drinking His blood is that if we hear Him, the words that He spoke, the Word of God from God, and believe those words and take them in and grow from them then we are eating Jesus. It is as He said,
63 It is the Spirit who gives life; the flesh is no help at all. The words that I have spoken to you are spirit and life.
The Catholic Church sees the passage as referring to the Catholic Communion where they say the bread and wine are turned into the body and blood of Jesus and that we must partake of that or we have no life in us. This is called the doctrine of transubstantiation and this was written in the Catholic Church in 1551, thus giving to the Catholic Church the power to give eternal life since they are the only ones whose priests can change the wine and bread to Jesus blood and body, or so the story goes. It is no coincidence that this doctrine was developed when the Reformation was in progress and people were leaving the RCC as they came to understand the Bible for themselves.
But of course the communion is symbolic of the last supper and the body and blood of Jesus and the New Covenant, the Passover feast being symbolic of the Mosaic Covenant.
The New Covenant is prophesied in the Old Testament and is a time when the Spirit of God is given to those who believe, thus Jesus said it is the Spirit who gives life; the flesh is no help at all.