This is a parting of the way. The believers remain and the non-believers depart. many choose to leave Jesus. it is Peter who makes the great assertion of his faith in Jesus who has the words of eternal life. He professes him as the "Holy One of God."
Note the title "Son of Man." This is Jesus' choice of description of himself. It has occurred already in this chapter. The meaning is ambiguous. It reflects Daniel's vision (Dan 7:13-14) alluding to a heavenly being with an active relationship between heaven and earth. It can also and often refer to the Aussie equivalent of "a bloke" or ordinary person. Jesus has the two meanings in mind.
"I gazed into the vision of the night, and I saw, coming on the clouds of heaven, one like the Son of Man." (Dan 7:13)
"It is the spirit that gives life, the flesh has nothing to offer." This clashed with the words of Jesus re: the necessity of eating the "flesh of the Son of man." It is not a denigration of our bodies because "the Word became flesh." There is a shift of meaning from unredeemed humanity to the humanity of Jesus.
The choice is ours. To leave with the 500 or to stay with Peter.