Let me suggest two ways we might apply this statement of fact.
First, I think it sheds some light on what might seem like Jesus' intransigence in preaching the Bread of Life Discourse. In John's account, Jesus doesn't seem particularly concerned about the consternation His teaching causes among His disciples -- and admit it, this teaching is tough to get your head around even if you're a daily communicant.
Catholics like to use this as evidence of the truth of the dogma of the Real Presence; if Jesus were speaking figuratively, the argument goes, wouldn't He correct His disciples' misinterpretation rather than let them return to their former way of life? But that argument leaves untouched an even more fundamental question: Whatever Jesus means, wouldn't He want His disciples to understand him rather than let them return to their former way of life? Wouldn't He want to be sure He communicated His meaning to those He is teaching?
And the answer to that more fundamental question is, No, not if He knew from the beginning the ones who would not believe.
That the bread Jesus would give is His flesh for the life of the world is a hard saying. But a disciple doesn't accept a saying based on his intellectual grasp of the saying, he accepts it based on his faith in his master. A disciple asks, "What does this saying mean?," not, "Who can accept it?" (Hint: a disciple can accept it.)
There would be plenty of time to answer His disciples' questions about the Bread of Life Discourse (I might try to carve out an hour or so for that this afternoon). During the conversation recorded in John 6, though, He wasn't really asked about His saying as such, He was asked about His authority as master. His authority is a matter of faith, so it sufficed for Him to assert it and let the faith fall where it may (i.e., on those to whom it is granted by His Father).
The second application follows from the first, and it is this: We aren't Jesus. We don't know from the beginning the ones who would not believe. We are not masters called to form our own disciples. Therefore, we don't get to be intransigent and unconcerned about the consternation caused by our preaching of the Gospel to every living creature. We ought to try to make ourselves understood, because we can't make ourselves masters.