These were not outsiders but people who had been following Jesus. Gill says they were "Not of the twelve, nor of the seventy, but of the multitude" of disciples. They found His words about eating His flesh too much to bear. Barnes explains that "hard" here means "offensive, disagreeable," and rejects the sense "difficult to be understood." Gill allows both: a saying open to objection, or one "difficult to be understood and received." Their question "who can hear it?" is really a statement: no one can be expected to accept this.

Jesus knew "in himself" that they murmured and answered with questions of His own: "Doth this offend you? What and if ye shall see the Son of man ascend up where he was before?" (John 6:61-62). He explained, "the words that I speak unto you, they are spirit, and they are life," but added, "there are some of you that believe not" (John 6:63-64). The exchange ended in a parting: "From that time many of his disciples went back, and walked no more with him" (John 6:66).

The Greek word for "hard" is sklēros, which Thayer defines as hard, harsh, rough, or stiff. Applied to a saying, as here, it means harsh and offensive. The "saying" is logos, "word." The question reads literally, "who is able to hear it?"

Barnes notes that the word "disciple" means "learner." In John 6 it covers more than the twelve. Many of these learners turned back, while the twelve stayed (John 6:66-67).

This verse marks a turning point in the chapter. The day before, the crowds wanted to make Jesus king (John 6:15). Now even many of His followers called His words unbearable. Barnes observes that some follow Jesus for "the prospect of some temporal benefit," and fall away when that benefit does not come. Gill says they left "finding that he would not be made king, nor set up for a temporal redeemer."

Jesus did not water down His words to keep them. Matthew Henry notes that "The Messiah's kingdom was not of this world," and they were to understand by faith "what he had said of a spiritual living upon him, and his fulness." The hard saying showed who was following Him for the bread and who was following Him for Himself.