What does John 6:64 mean?

Sadly, not all people who "follow" Jesus actually "believe in" Jesus. The story told in this chapter vividly illustrates this unfortunate truth. Crowds gathered around Him due to His miracles (John 6:2). They were so impressed by His feeding of thousands that they were ready to make Him a king (John 6:15). And yet, when Jesus explains that entertainment and free food are not His real ministry, they are unimpressed (John 6:41). The more He insists on a spiritual, personal meaning behind His miracles, the angrier they become (John 6:52). Eventually (John 6:65–66), many of these shallow "followers" will leave, proving they are not "believers."

There is a profound difference between being attracted to aspects of Christianity versus being a born-again Christian. Actions not grounded in legitimate spirituality are pointless. Typically, the difference emerges when a Christian message conflicts with a person's preferences. Nearly all those who turn away from Jesus after following Him do so in response to some disappointment, frustration, or limitation. In this case, most of the people hearing Jesus' message don't like it. That causes them to abandon Him. As Jesus said in the prior verse, "the flesh is no help at all."

Peter, on the other hand, expresses the attitude of an actual "believer" in Christ. Whether he likes what he hears or not, he knows that Jesus is the Truth (John 6:68–69). Instead of rejecting Jesus because Jesus challenges his thinking, Peter submits to a higher truth than his own.

Here, Jesus is speaking to His "disciples" in a broad sense. In context, this term refers to all the people who have been tagging along and listening to His teaching. The core group of twelve men, on the other hand, will be specifically addressed after many of these other "disciples" turn and walk away.