"... but he who feeds on this bread will live forever." (John 6:53-59)

"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. For my flesh is real food and my blood is real drink. Whoever eats my flesh and drinks my blood remains 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. This is the bread that came down from heaven. Your forefathers ate manna and died, but he who feeds on this bread will live forever." (John 6:53-59) 

Are they supposed to literally eat Jesus' flesh and drink his blood?

Jesus is not speaking of people literally eating his flesh and drinking his blood. Such an interpretation - made by many - is grotesque. Such an interpretation is inaccurate and unrealistic.

Here Jesus continues with the metaphorical use of bread and eating, which also completely confused many of the institutional temple priests who had assembled to hear him in a synagogue in Capernaum. This is evidenced in the previous verse:
Then the Jews began to argue sharply among themselves, "How can this man give us his flesh to eat?" (John 6:52)
This illustrates that Jesus, who was teaching in a synagogue as would a Rabbi of those times, was using an analogy that many in his audience did not understand. In John 6:44-51, Jesus describes that the loving servant of God supplies the "food" that ultimately satisfies the spirit-person (each of us). Was Jesus speaking of physical food? No.

Was Jesus speaking literally?

Jesus clearly differentiated from physical food by saying that this "bread of life" enables one to live forever. Yet the crowd did not understand. In fact, John describes that many of Jesus’ disciples left him during this sermon, saying:
“This is a hard teaching. Who can accept it?” (John 6:60)
From this time many of his disciples turned back and no longer followed him. (John 6:66)
Just as he was not talking about physical food, Jesus was not talking about people actually eating the flesh of his physical body. He was not talking about people drinking the blood of his physical body. Just as he used the bread symbolically as an analogy, his is using his flesh and blood symbolically. Jesus certainly was not promoting cannibalism.
"The Spirit gives life; the flesh counts for nothing. The words I have spoken to you—they are full of the Spirit and life." (John 6:63)

What does 'eat the flesh of the Son of Man and drink his blood' symbolize?

"Flesh" symbolized Jesus' teachings, and "blood" symbolizes his relationship with God. 

The word "flesh" is being translated from the Greek word σάρξ (sarx), which can mean "flesh" but also, according to Strong's lexicon, "as the symbol of what is external." Jesus assumed a physical body of flesh in order to give us his teachings. These are the external elements of Jesus.

"Blood" is being translated from the Greek word αἷμα (haima). This can mean blood when used literally, but when used metaphorically, can mean "the seat of life" as this is what blood was considered back then. Jesus is thus referring to his essence - the core of his being, which is his relationship with God.

Jesus' used his life to serve God. He also taught others to love and serve God. This was his primary mission. Therefore, to be taking Jesus' teachings to heart and following them would mean that one would also begin loving and serving God. 

By loving and serving God, we are partaking of the spiritual food Jesus is speaking of, and his very being, because Jesus' mission and purpose was to turn lovers of mammon to lovers of God.

As for "son of man," remember that the Greek word translated to “son” is υἱός (huios). This is more appropriately defined, as taken from the Greek lexicon, to be "used to describe one who depends on another or is his follower."Thusυἱόςwould be moreappropriatelytranslated as loving servant.

Thus with the Greek phrase υἱὸς τοῦ ἀνθρώπου, Jesus is referring to himself as the servant of humanity, becauseτοῦ ἀνθρώπου is translated to either "of man" or "of mankind" or "of humanity."

To describe oneself as the "servant of humanity"is a humble self-description, consistent with Jesus' other teachings, such as when he washed the feet of his disciples and told them:
"Instead, whoever wants to become great among you must be your servant"(Mark 10:43)
Thus we know that Jesus felt himself to be the servant of others, as he gave them God's message.

This self-description is consistent with other servants of God also describing themselves (or God referring to them) as "servant of humanity," (mistranslated as "son of man"). Consider David's statement to God about himself:
"O Lord, what is man that you care for him, the son of man [servant of humanity] that you think of him?" (Psalms 144:3)
While creative and speculative ecclesiastical commentators on the Bible say that David is referring to Jesus, this would be wholly inconsistent with the text before and after this statement. David was communing with and praising God, while discussing his relationship with God.

Furthermore, God called Ezekiel the "son of man" [servant of humanity] at least 60 times in the Book of Ezekiel. Job also referred to himself as a "son of man" [servant of humanity].

The loving servant of God is also the servant of all of humanity because his mission is to deliver God’s message, which, if heard clearly, serves to deliver us back to our original relationship with God.

What is the 'bread that came down from heaven'?

Jesus is referring back to his statement in John 6:32.

"This is the bread that came down from heaven" because Jesus has humbly surrendered his life to God, and is enjoying a loving relationship with God. This relationship with God is "bread" or "food" because this sustains him.

If we assimilate Jesus' devotion by reading and carefully reviewing his teachings and doing our best to establish our own loving service relationship with God, we would effectively be 'consuming' this "bread that came down from heaven."

This is speaking of spiritual consumption - the understanding of those teachings and the acceptance and following of those teachings.

The key part of Jesus' statement illustrating this analogy is:
“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.”
What do sending and feeding have in common? The "bread of life" that Jesus is delivering is the teachings of God’s message. Hearing those teachings, and following in Jesus’ footsteps by devoting our life to God is the feeding.And what is the substance of the core teaching and example of Jesus?
“ ‘Love the Lord your God with all your heart and with all your soul and with all your mind.' This is the first and greatest commandment."(Matt. 22:37-38)
And finally, how does this relate to: "and I will raise him up on the last day"? Does this relate to some far off day in the future where the world will end and Jesus will come down riding a big horse to round up all those who are waiting (some for thousands of years apparently)? This "world is coming to an end" thesis has been proposed and abused by ecclesiastical sectarian teachers for centuries. Quite simply, this is a misinterpretation of Jesus' teachings.

What does 'the last day' mean?

"The last day" is quite simply the day that each of our bodies dies and we each leave our body. We each will have a unique last day as our physical body dies. On this day, we are torn away from our family, our possessions, our reputation, and all our plans.

Also on this day our next destination is determined. If we have continued to live lives of self-centeredness, focused upon our own pleasure, we will not be raised up by Jesus. We will remain in this hellish physical world, away from God.

If, however, we take the teachings of Jesus into our hearts, and learn to love and serve the Supreme Being as Jesus taught and showed us, then yes, Jesus will raise us and escort us back to the spiritual dimension after the death of our physical body.

This is what is meant by "will live forever."