"but when they saw him walking on the lake, they thought he was a ghost. They cried out, because they all saw him and were terrified. Immediately he spoke to them and said, 'Take courage! It is I. Don't be afraid.' Then he climbed into the boat with them, and the wind died down. They were completely amazed, for they had not understood about the loaves; their hearts were hardened." NIV translation
The disciples did not recognize Jesus and so cried out in fear. The same type of thing happens in our lives many times. If we are not looking to see God at work in our lives, we will not recognize His hand and we may think that we are alone. He calmed them and the wind down but we see they did not understand what had happened. A hardened heart can not feel and we see here that their hearts were hardened concerning the things that they had seen Jesus do. They had seen the multiplication of the loaves and fishes but did not let it sink into their hearts and change their understanding of Jesus and the natural world.
"When they had crossed over, they landed at Gennesaret and anchored there. As soon as they got out of the boat, people recognized Jesus. They ran throughout that whole region and carried the sick on mats to wherever they heard he was. And wherever he went - into villages, towns or countryside - they placed the sick in the marketplaces. They begged him to let them touch even the edge of his cloak, and all who touched him were healed." NIV translation
People brought their loved ones from all over the region to be healed. Everyone that touched Jesus was healed and it reminds us that all who come to Jesus will be healed spiritually and saved for eternity. These people did not understand this yet but they acted in faith with what they knew. They had heard that this man could heal their loved ones physically and they believed it and took action. This, too, would have been a lesson and an encouragement to the disciples as they were being stretched in their faith. Likewise, Jesus asks us to live out our faith because when we put it into action we will grow.