Here was a man of authority. An authority given to him by his superiors and one which was recognised and acted upon by those in the shop. He said something and it was agreed with and acted upon immediately. Jesus said the words, the storm subsided and everything was calm. Here we have Jesus' authority over nature.
Faith can chase out fear, or fear can chase out faith.
Jesus chastises his followers because they have failed to trust in God. Jesus' mission would not be ended by drowning in a freak storm. When he died it would be in accordance with God's pre-ordained plan. It is no use having a plan if you do not have the means to carry it out. This reminds us of God's power over nature.