Mark 4.39-41: And he awoke and rebuked the wind and said to the sea, “Peace! Be still!” And the wind ceased, and there was a great calm. (40) He said to them, “Why are you so afraid? Have you still no faith?” (41) And they were filled with great fear and said to one another, “Who then is this, that even the wind and the sea obey him?” (ESV)
The context of these verses is a trip across the Sea of Galilee Jesus directed his disciples to take. Jesus said, “Let us go over to the other side.” (NASB). So we can know very well that they were going to make it across, even though a great storm arose and filled their boat with water to the point of sinking.
Prior to this trip Jesus told his disciples in Mark 4.11 that, “To you has been given the mystery of the kingdom of God,” (NASB). The word mystery in this case means things not previously known, but that can be understood when they are made known. So very early in Jesus’ ministry he tells his disciples that they are going to learn profound truths about the kingdom of God that most people won’t learn in the way they are going to learn them. The events of this trip are an example of the revelation to the disciples that Jesus is God.
Psalm 65.7 speaks of God as the one who “stills the roaring of the seas, the roaring of their waves, the tumult of the peoples” (ESV). Jesus revealed to his disciples by speaking to the waves and their obedience to him, that he is God. At that moment the disciples didn’t understand all that had taken place, but they would do so in the future.