“hard” = skleros = hard to the touch or rough. It comes from a root meaning “dry.”

It was not so much that what Jesus had said was hard to understand; it was that what He had said was hard to accept. Calvin commented that “the hardness was in their hearts and not the saying.”

“Who can accept it?” (NIV) = “Who can hear it?” (KJV) = “Who can stand to hear it? – Who can be expected to listen to such teaching?” (Amplified)

The disciples undoubtedly found the teaching to be perplexing, but, as Morris comments, “it was the part they could understand rather than the part they could not that bothered them.” (383) Barclay says that “to this day many a man’s refusal of Christ comes, not because Christ puzzles and baffles his intellect, but because Christ challenges and condemns his life.” (qt’d in Morris 383)