See John 6:53-58
"How can this man give us his flesh to eat?" (John 6:52) Thinking Jesus was speaking literally, the crowd's question is natural. (Remember that they were already confused by Jesus' words that he came down from heaven when in fact they knew he came from Nazareth.) The theme of Jesus' teaching throughout this dialogue is the giving of himself as the perfect sacrifice resulting in eternal life for all who believe.
So he continues: "I tell you the truth, unless you eat the flesh of the Son of Man and drink his blood, you have no life in you. Whoever eats my flesh and drinks my blood has eternal life, and I will raise him up at the last day." (vs 53-54) Those words harmonise with what he said earlier: "For my Father's will is that everyone who looks to the Son and believes in him shall have eternal life, and I will raise him up at the last day." (vs 40) Both these Scriptures are saying the same thing. "Eternal life" and being "raised up at the last day" come from eating and drinking his flesh and blood which is done through faith, through trusting the sacrifice of Jesus. As sinners we look, in faith, to the sacrifice of Jesus for eternal life. Our trust, our faith is in what he has done for us.
"For my flesh is real food and my blood is real drink." (vs 55) Jesus is affirming that he is the perfect sacrifice. All the animal sacrifices previously offered could never do what the sacrificed body and blood of Jesus would do. "Whoever eats my flesh and drinks my blood remains in me and I in him." (vs 56) In other words, the closest possible fellowship will exist between the saviour and the saved ("[he] in me and I in him"). "Just as the living Father sent me and I live because of the Father, so the one who feeds on me will live because of me." (vs 57) How does one "feed" on Jesus? The Lord has provided the answer: "He who comes to me will never go hungry, and he who believes in me will never go thirsty." (vs 35) We feed on Jesus by coming to him in faith, by believing in him as the perfect Lamb of God whose death secured eternal life. We live a life of faith in him from the moment of our conversion until we die. That is how we are nourished spiritually.
"This is the bread that came down from heaven. Your fathers ate manna and died, but he who feeds on this bread will live forever." (vs 58) Jesus is declaring that his place of origin is heaven, not Nazareth as some had supposed. And unlike their ancestors who ate the manna and died, Jesus has come down from heaven as the bread of life and all who eat this bread will live forever. The new life they will have is not physical, but spiritual.
His words were heard by an unreceptive audience and his disciples grumbled. To clarify his words Jesus said to them, "What if you see the Son of Man ascend to where he was before?" (vs 62) In other words, if you see me going back to where I came from, namely heaven, then you will know that I came down from heaven.
Even if it was possible, and it's not, to eat Jesus literally, one would not obtain eternal life by doing so. We eat and drink his body and blood through faith, by believing, by trusting in his death upon the cross. Knowing how his audience were misunderstanding him, Jesus gave further clarification: "The Spirit gives life; the flesh counts for nothing. The words I have spoken to you are spirit and they are life." (vs 63) We have two conflicting views: what Jesus said and the understanding of his audience: "the Spirit gives life" said Jesus, and "the flesh counts for nothing." The question had been asked earlier, "How can this man give us his flesh to eat?" (vs 52) They were thinking, incorrectly, that Jesus would literally distribute himself for them to eat and drink. Such a literal understanding is incorrect; "the flesh counts for nothing." What flesh counts for nothing? The literal flesh that they thought he would give them. But Jesus says that a literal eating of his flesh would count for nothing. Eternal life cannot be imparted in this way. Rather, "It is the Spirit that gives life."
They Walked With Him No More
Many who had come to Jesus now turned and walked away. (Their reaction was like that of the rich ruler who disliked what Jesus said and walked away. See Matthew 19:22) Jesus never called them back. Why? Because "Jesus had known from the beginning which of them did not believe…" (vs 64) There were no honest seekers among those who walked away that day. Jesus then asked the Twelve, "You do not want to leave too, do you?" (vs 67) And Peter replied, "Lord, to whom shall we go? You have the words of eternal life." (vs 68) Peter is saying that there is no other saviour. Eternal life is contained in the words of Jesus, who has shown that man's spiritual need can only be satisfied through the sacrifice of the body and blood of Jesus. And all who believe in Jesus, all whose faith embraces his sacrifice, are said to eat the flesh and drink the blood of Jesus, resulting in eternal life.