Terrific thread! One note to DMP, however, Christ defined what eating his flesh and drinking his blood meant:
Jesus declared, "I am the bread of life. He who comes to me will never go hungry, and he who believes in me will never be thirsty." John 6:35
Going to Jesus is our spiritual food. Believing is our spiritual drink. He takes care of the rest. The discussion which follows (and precedes, starting with verse 25), is all explanatory regarding this one verse, I think. Impatient and a bit angry on the part of Jesus, but nevertheless explanatory.
It is fascinating to compare this exchange he has in this section of John 6 with His earlier conversation with Nicodemus in John 3. Nicodemus was looking for the truth, while His discussion with the Jews in 6 shows they were only looking to argue and He met them on their ground and upped the ante.