What did Jesus mean when He said we must "eat His flesh and drink His blood"? In John 6, Jesus states that unless we eat His flesh and drink His blood, we have no life in us: 


  Jesus said to them, “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 6:53-58 NIV)


Could this have been a reference to the Passover Lamb of which the Israelites were supposed to eat all of it?  What  is the common Protestant understanding of this?  Do some traditions associate this with Communion?
We often let ourselves get trapped by not searching for other Scriptures which may help to explain what we do not fully understand.

This particular scripture is complicated by the part following which denotes his following lessening, because they did not understand that Jesus was not speaking of literally eating his flesh and drinking his blood. Today after knowing all about his death and resurrection understand that.

Jesus being an eternal being would have seen all of his teachings as if they were one continuous diatribe. Therefore we must consider all of his teaching at once. the following are some of his sayings which give meaning to this particular Scripture.

All Scripture is quoted from the King James translation, unless otherwise noted.


  John 6:35  And Jesus said unto them, I am the bread of life: he that cometh to me shall never hunger; and he that believeth on me shall never thirst. 


This Scripture gives meaning to eating his body and drinking his blood, and we need to also remember the reason we eat and drink in the first place. Our reason for eating and drinking is to sustain life. The same is true of our spirit and our eternal life. If we are to remain in consonance with Jesus teachings we need to continue to feed that spirit in order to keep it alive and well.


  John 6:32 and 33 Then Jesus said unto them, Verily, verily, I say unto you, Moses gave you not that bread from heaven; but my Father giveth you the true bread from heaven. 33  For the bread of God is he which cometh down from heaven, and giveth life unto the world.


It is quite obvious that Jesus is not talking about Worldly bread, as the Manna and quail which Moses asked of God; but is referring to Spiritual bread. All of these saying were in direct response to his disciples.


  John 6:28 through 31  Then said they unto him, What shall we do, that we might work the works of God? 29  Jesus answered and said unto them, This is the work of God, that ye believe on him whom he hath sent. 30  They said therefore unto him, What sign shewest thou then, that we may see, and believe thee? what dost thou work? 31  Our fathers did eat manna in the desert; as it is written, He gave them bread from heaven to eat. 


It probably frustrated Jesus that they could not put together his teachings to understand, and it must still frustrate him, that we cannot understand; even today with all of his word condensed into the Gospels. Which is probably why he said:


  John 14:26  But the Comforter, which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you. 


For them they had been with him during his teaching, however we did not have that privilege, and must study the Scriptures in order to connect all of his teaching.

It would have been necessary that they completely remember and understand his teachings since they would be tasked with passing them on to posterity, in written form.

Hope this helps