What does John 6:67 mean?

At the height of His earthly popularity most of the people who had been learning from Jesus walk away (John 6:66). They completely abandon His teachings and His ministry. They do not like what He has taught (John 6:60), so they choose their own preferences over the truth. This illustrates the enormous difference between those who show interest in Christianity versus those who are true believers in Jesus Christ. Hanging out with the crowd and applauding at miracles is not the same as accepting Christ as one's Savior. As soon as the "followers" were put under pressure, they proved that they were not "believers" by walking away.

That context makes this verse important. Jesus now asks the twelve members of His inner circle whether they plan to leave also. What's curious about this is that one of them, Judas, is not a believer either (John 6:71). Challenge and trial don't always separate out every possible non-believer.

This also makes Peter's statement about the faith of these twelve men a bit presumptuous. Peter will claim that "we," meaning these twelve men, have legitimate faith in Christ. But at least one of them does not; Peter does not know as much as he thinks he does.