In Mark chapter 6, we see the miracle of Jesus walking on the water. There is an interesting commentary there by Mark - Mark 6:52 " for they had not understood about the loaves; their hearts were hardened." When Jesus walked on the water and then calms the seas, the disciples were astonished. They were surprised because Jesus was going beyond their expectations or comprehension of the physical world. And in that moment, Mark makes a comment that they did not understand about Jesus or his ministry.