John 6:41-59
41 So the Jews grumbled about him, because he said, “I am the bread that came down from heaven.” 42 They said, “Is not this Jesus, the son of Joseph, whose father and mother we know? How does he now say, ‘I have come down from heaven’?” 43 Jesus answered them, “Do not grumble among yourselves. 44 No one can come to me unless the Father who sent me draws him. And I will raise him up on the last day. 45 It is written in the Prophets, ‘And they will all be taught by God.’ Everyone who has heard and learned from the Father comes to me— 46 not that anyone has seen the Father except he who is from God; he has seen the Father. 47 Truly, truly, I say to you, whoever believes has eternal life. 48 I am the bread of life. 49 Your fathers ate the manna in the wilderness, and they died. 50 This is the bread that comes down from heaven, so that one may eat of it and not die. 51 I am the living bread that came down from heaven. If anyone eats of this bread, he will live forever. And the bread that I will give for the life of the world is my flesh.” 
52 The Jews then disputed among themselves, saying, “How can this man give us his flesh to eat?” 53 So Jesus said to them, “Truly, truly, I say to you, unless you eat the flesh of the Son of Man and drink his blood, you have no life in you. 54 Whoever feeds on my flesh and drinks my blood has eternal life, and I will raise him up on the last day. 55 For my flesh is true food, and my blood is true drink. 56 Whoever feeds on my flesh and drinks my blood abides in me, and I in him. 57 As the living Father sent me, and I live because of the Father, so whoever feeds on me, he also will live because of me. 58 This is the bread that came down from heaven, not like the bread the fathers ate, and died. Whoever feeds on this bread will live forever.” 59 Jesus said these things in the synagogue, as he taught at Capernaum.

Jesus tries to instruct the synagogue leaders but they continue in their obtuse and really staunch hold on their unbelief. And that is exactly what Jesus is addressing here - our belief. Some see this section as a reference to the Lord’s Supper, but it cannot be, because the Lord’s Supper was not yet instituted. This section is an extension of the Bread of Life declaration. Jesus is continuing the thought expressed already in verses 29 and 40: he who believes will live.

The important issue is life, the life that comes from God and is eternal. When the heavenly Father sent his Son into this world, he gave him that life also in his human nature. That’s why Jesus could say, “I live because of the Father.”

Similarly, when a person eats of (believes in) Jesus, that person lives because of Jesus. That same life, which is the very essence of life in God, passes on to each believer. To summarize and close his talk, Jesus repeated the comparison he made earlier with the manna (verses 49, 50). Those who heard Jesus that day did not misunderstand him. He made sure of it by continually returning to key thoughts. Each of the following repeats several times:
Jesus is bread.
Jesus, the bread, came down from heaven, sent from the Father.
Whoever eats the bread, that is, believes in Jesus, has eternal life
Jesus will raise that person up at the Last Day.

While the vernacular in this passage is difficult (eating flesh and drinking blood) we have to keep Jesus' true message it mind. It's about BELIEF in Him. He is all that we need.