The account ends with a comment about the disciples’ lack of understanding. This was not because they lacked the opportunity to believe in Jesus. They had seen the miracle of the loaves and many other miracles.
Instead, their hearts were too hard (they were not open to understanding). This is usually a quality of those who oppose Jesus (for example, 3:5; see also 8:17, 21; 9:32).
Later, their hearts would be changed. They would come to understand these things (Luke 24:44–49; John 12:16; 13:7).