Just read this from my Porterbrook Theology study, and had to share it.
On that day, when evening came, He said to them, “Let us go over to the other side.” 36 Leaving the crowd, they took Him along with them in the boat, just as He was; and other boats were with Him. 37 And there arose a fierce gale of wind, and the waves were breaking over the boat so much that the boat was already filling up. 38 Jesus Himself was in the stern, asleep on the cushion ; and they woke Him and said to Him, “Teacher, do You not care that we are perishing ?” 39 And He got up and rebuked the wind and said to the sea, “Hush, be still.” And the wind died down and it became perfectly calm. 40 And He said to them, “Why are you afraid ? Do you still have no faith ?” 41 They became very much afraid and said to one another, “Who then is this, that even the wind and the sea obey Him?”
Jesus does not simply stop the storm, He stills the waves. In a storm, when the wind drops, the waves keep going for a while. But Jesus stops them immediately. All the energy in the waves dissipates in an instant. According to Psalm 89:8-13, only God has the power to control the sea.
O LORD God of hosts, who is like You, O mighty LORD ? Your faithfulness also surrounds You. 9 You rule the swelling of the sea ; When its waves rise, You still them. 10 You Yourself crushed Rahab like one who is slain ; You scattered Your enemies with Your mighty arm. 11 The heavens are Yours, the earth also is Yours; The world and all it contains, You have founded them. 12 The north and the south, You have created them; Tabor and Hermon shout for joy at Your name. 13 You have a strong arm ; Your hand is mighty, Your right hand is exalted.- Psalm 89:8-13
So Mark is telling us that Jesus must have the authority of God Himself. He (Jesus) can still the sea with a word because He (God) made the sea with a word. Or rather, Jesus was the Word with which God made the sea (John 1:1-3).
In the beginning was the Word, and the Word was with God, and the Word was God. 2 He was in the beginning with God. 3 All things came into being through Him, and apart from Him nothing came into being that has come into being. – John 1:1-3