This chapter from John is not at all primarily about the Eucharist; that is strictly an interpretation that only came to us once we had seen, accepted, and come to cherish that Eucharistic miracle of God's love.  Seeing this chapter only in that manner has obscured for us what the whole chapter is actually about, which is whether people can accept Christ's divinity or not. 

The last lines of today's Gospel are either vain and empty hyperbole on Christ's part or a fairly clear claim to a power and a love that only God can have, and so He is asking the people whom He had just miraculously fed --- and is asking us as well --- to take Him seriously, but it would not have been easy for a people who had struggled long, hard, and painfully to reach monotheism to even grasp what Christ was trying to say, that He was not only fully human but was also the God who lived so carefully hidden in the inner depths of the Temple --- and both of them at the same time!

In the end most people can't do that, not then, as the end of John's sixth chapter shows, and certainly not today.  Even the apostles had no idea what Christ actually meant --- but at least they were willing to stick around to find out. 

We need to join them in their trust, for as Oswald Chambers, a Protestant pastor of the nineteenth century, once said, “Faith never knows where it is being led, but it loves and knows the One who is leading.”