The apostles saw a great miracle. And even they, who had seen so many miracles and even had their own family members healed, could not yet conceive of who was with them.
Mark 4:40“And He Himself was in the stern, asleep on the cushion; and they awoke Him and said to Him, “Teacher, do You not care that we are perishing?” And being aroused, He rebuked the wind and said to the sea, “Hush, be still.” And the wind died down and it became perfectly calm. And He said to them, “Why are you so timid? How is it that you have no faith?” And they became very much afraid and said to one another, “Who then is this, that even the wind and the sea obey Him?””
It was Jesus, the Son of God, God with Us, God in the flesh. The answer was in scripture, once they put it together.
Ps. 65:7“Who stills the roaring of the seas, The roaring of their waves, And the tumult of the peoples?”
Ps. 89:9“You rule the swelling of the sea; When its waves rise, You still them.”
Ps. 107:29“He caused the storm to be still, So that the waves of the sea were hushed.”
Yes, the answer to the question of amazement was thrice before given in scripture. They just hadn’t put their question and the information God already provided together — just like so many times today.