Joh 6:40 - 42 "For this is the will of my Father, that everyone who looks on the Son and believes in him should have eternal life, and I will raise him up on the last day." So the Jews grumbled about him, because he said, "I am the bread that came down from heaven. 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'?" 

Jesus had come to live in the will of Father God, just as He always existed, at One with the Father and Spirit. 
He was from the beginning the very initiator of all creation. The will of God is very clear looking on the creation as a reflection of God's handiwork, the handiwork of Yahweh- of Jesus The Son, in that view believing and receiving Him as King and Lord of the universe and of me. In Him we find life and life beyond our temporary existence on earth. He is the bread the very sustenance of life and the Jesus of Nazareth is a human being yet He has existed for eternity and has come to us here from being eternally from God. He was with God and is God.
So you can either believe in Him and what He has said and done or you can castigate a deride Him as delusional, but you cannot remain neutral towards Him. He holds your future within Himself. He has all authority over His creation. He is Absolutely Sovereign. He is Absolute Love.

This claim left the religious nonplussed. They set to deny His claim and make Him a mockery. He told them plainly; "Everyone who really has a connection to God and has listened and heard the Word of God, they will for sure come to me and believe."
"Though no one has ever seen God the Father, they have seen Him in Me"; Jesus Declared! "I Am from Him and One with Him."

Joh 6:43 - 46 "Jesus answered them, "Do not grumble among yourselves. No one can come to me unless the Father who sent me draws him. And I will raise him up on the last day. 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-- not that anyone has seen the Father except he who is from God; he has seen the Father." 

Jesus wasn't mincing words or holding back in any manner. Jesus took them back to their desire to have a leader like Moses again. He told them in no uncertain way that He was greater than Moses and He Himself provided the manna, now that He was here they could be consumed and filled with His presence if they only would believe. He was here to give grace and fulfill the commands that He personally gave to Moses on the mountain.

Joh 6:47 - 51 "Truly, truly, I say to you, whoever believes has eternal life.  I am the bread of life.  Your fathers ate the manna in the wilderness, and they died. This is the bread that comes down from heaven, so that one may eat of it and not die.  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." 

The religious elite couldn't understand, they had no spiritual insight. They were focused on the physical and there place in this world. They had no real connection to the spiritual world. It was all rules and ritual a facade of worshiping their own abilities and positions. 

Joh 6:52  "The Jews then disputed among themselves, saying, "How can this man give us his flesh to eat?" 

Jesus became even more emphatic, more graphic. They would either get or not but Jesus was going to be very clear. 
My presence here my body and the overflow of my heart must consume your desires and fulfill your needs then you or you won't live, you have no chance at truly being alive. I am the true sustenance for your life and I will quench and fulfilled your needs. If you believe Me and receive what I say, I will be one with you and the Fathers' love will engulf you with grace and forgiveness. 
I Am eternal life and just as Father God is self existent with no need in Himself, I Am self existent. I overflow with life and satisfaction to complete fulfillment to those who live in Me. If you feed yourself with Me and drink your fill in Me, you will be fully alive now and forever. 
Jesus said all of this when He was among the religious elite. In the place of worship. He was where He should have been most welcome and honored, but the didn't recognize Him or accept what He said to them. They rejected the very God who they claimed to worship in that place. 

Joh 6:53 - 59 "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. Whoever feeds on my flesh and drinks my blood has eternal life, and I will raise him up on the last day. For my flesh is true food, and my blood is true drink.  Whoever feeds on my flesh and drinks my blood abides in me, and I in him. 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. 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. Jesus said these things in the synagogue, as he taught at Capernaum."