But he said to them, "I AM. Don't be afraid."
This wonder contrasts dramatically with another wonder of stilling the tempest  (Matthew 8:23-27).  In that situation, Christ was on board; here he was not.  There he was asleep; here he was in the mountain praying.  There they were afraid of the winds and waves; here they were afraid of Jesus. There he rebuked the winds and waves; here they responded to his will without an audible command.  In both situations, the only safety of the disciples was in the will of Christ.