After Jesus fed five thousand men with a little food, He had a rendezvous with His disciples, where He walked on the Sea of Galilee to meet up with them. Then John veers off from the other three Gospels, back into the doctrine-rich speeches and dialogs with Jesus found so often in John.
John 6:25-59 imparts to us a dialog in which Jesus refers to Himself as the bread of life. However, this does not appear to be a dialog in the sense of an actual recorded conversation, but rather a dialogue in the sense of the literary style used by Greek philosophers to advance their arguments, like we find in Plato's The Republic.
The episode begins with the people who Jesus had fed (during the miracle where Jesus had fed five thousand people with a little bread and a couple fish) catching up to Him in Capernaum. Jesus tells them that they are looking for Him because they had eaten for free, not because He had worked miracles. He then tells them to work for food which will yield eternal life, which is given by the God-endorsed "Son of Man" (John 6:25-27). (Of course, Jesus meant Himself by the "Son of Man," making it a rather odd conversation by having Jesus speak of Himself in the third person, but it is not uncommon with what we see elsewhere in the Gospels.)
These people reply, asking Jesus what work does God require. He replies that they must believe in the one God has sent (John 6:28-29). Again, Jesus replies in the awkward third-person perspective. Yet, this is good news! All you need to do is believe Jesus and eat His magic food to be Saved!
Can you guess what they would ask Jesus next? Would it be the logical "so, are you the one God has sent?" Or how about "can you tell us who this 'Son of Man' is that we may believe in Him?" Or maybe even "can you give us this food for eternal life?" Well, it is none of the above, but somewhat close to the first question. In John 6:30-31, we find:
So they asked Him, "What miraculous sign then will you give that we may see it and believe you? What will you do? Our forefathers ate the manna in the desert; as it is written: 'He gave them bread from Heaven to eat.'" NIVIt appears that they have have managed to conclude that Jesus is talking about Himself, so they ask Jesus to perform a miracle to prove Himself, yet supposedly they are the ones who had already experienced a miracle from Jesus first hand, being part of the feeding of the five thousand. That does not make sense, unless, for some unknown reason, nobody mentioned to them that five thousand men (including themselves) had been fed with only five loaves of bread and two fish.
However, it is equally unlikely that they mention the manna given to the Israelites by God during their Exodus (Exodus 16). Implicitly, this is a suggestion of a sign that Jesus could do to prove Himself. However, manna was not a sign, but rather a test given by God to see if the Israelites would obey Him (Exodus 16:4).
So we have a doubly unlikely response, at least if this is real dialog, but because it is a philosophical dialogue instead, their reply provides a convenient segue for Jesus to touch on the Old Testament teachings. Jesus tells them that Moses did not give them the bread from Heaven, but God gives the true bread in the form of the He who comes from Heaven to give life (John 6:32-33). Jesus is essentially saying that the Law of Moses will not grant eternal life, in highly figurative language.
They forget about needing a sign, and simply ask Jesus to give them "this bread" from now on (John 6:34). Far from being lost in the metaphor, they seem to have picked up on the fact that "this bread" of life is some sort of new teaching or law from God.
Jesus replies that He is the bread of life from Heaven, and that those who seek Him will never be hungry or thirsty. However, He knows that they do not believe Him (despite following Him around and asking for the bread of life). Jesus comes to do the will of God; that is to grant eternal life on the "last day" to whoever God sends to Jesus to believe Jesus (John 6:35-40). So Jesus is essentially telling them that because they do not believe Him, they will not receive the bread of life, just not in a very clear way.
Instead of being indignant about their exclusion, they grumble about Jesus; asking He could have come from Heaven when they knew His earthly family (John 6:41-42). They got hung up on this saying now, despite the fact that Jesus had just effectively stated the same fact in the previous reply in John 6:33. So we go from them apparently understanding Jesus to not understanding Him, but that is not as interesting as another slip in the reply...
This group of people are now called "the Jews" (John 6:41). So we have a supposedly Jewish eyewitness recording an event which happened within a Jewish population in a Jewish town, and yet feeling the need to specify that "they" were Jews. That would be like an U.S.A. native news anchor speaking of an event in Washington D.C. and specifying something that "the Americans" said. It is a tell of another authorship, who is likely not Jewish.
Moving on, Jesus tells them to stop their whining, and reiterates that He will only Save whoever God sends to Him (which was not what they were grumbling about). Jesus goes on to say that those who listen to God will come to Jesus, that only He has seen God, and that He will Save all who believe Him (John 6:43-47).
It is important to take a moment to highlight that Jesus is telling "the Jews" this information despite knowing that they do not believe Him, which, as He knows, means that they are not led by God to Jesus and therefore not destined to be Saved. So Jesus is essentially giving them all of this information to spite them, rubbing their noses in the fact that they will not partake of the bread of eternal life.
Jesus continues in His reply with information more fitting of the Jews' previous question regarding miracles and manna. He tells them that their forefathers ate manna, but they died. However, Jesus is the bread from Heaven, of which if anyone eats His flesh, they will live eternally (John 6:48-51).
Obviously, even the Saved will die physically. So by Jesus contrasting those who ate manna as being dead versus those who eat His flesh having eternal life, the implicit message their dead forefathers do not have eternal life, meaning that nobody who lived before Jesus' time can be Saved. Yet we find the manna-eating Moses surviving contemporaneously in eternal life in the Gospels (Matthew 17:3, Mark 9:4, Luke 9:30).
The Jews grumble again (John 6:52).
Jesus reiterates that they need to eat His flesh and drink His blood in order to have eternal life (John 6:53-56). Jesus lives because of God, and people who feed on Jesus will also live, forever, as opposed to those who ate the manna (John 6:57-59). So the message is concluded with text that clearly indicates that the eating of Jesus is not a literal task, despite tying in the literal example of the Israelites eating manna. No transubstantiated communion wafers are required for Salvation.
John's message of Jesus' message here is that you need to seek out Jesus with the same level desire and necessity that you do your daily nourishment, if not greater, because then you will be rewarded with eternal life. Presumably, because John wanted to make Jesus appear other-worldly, or somewhat cloaked in divine mystery and possessing a higher knowledge, he instead chooses to butcher a message which could have written so simply that anyone could have understood it.