A.T. Robertson Commentary Mark 4:41

"And they feared exceedingly, and said one to another, Who then is this, that even the wind and the sea obey him?" — Mark 4:41 (ASV)

They feared exceedingly (εφοβηθησαν φοβον μεγαν). Cognate accusative with the first aorist passive indicative. They feared a great fear. Matthew 8:27 and Lu 8:22 mention that "they marvelled." But there was fear in it also.

Who then is this? (Τις αρα ουτος εστιν; ). No wonder that they feared if this One could command the wind and the waves at will as well as demons and drive out all diseases and speak such mysteries in parables. They were growing in their apprehension and comprehension of Jesus Christ. They had much yet to learn. There is much yet for us today to learn or seek to grow in the knowledge of our Lord Jesus Christ. This incident opened the eyes and minds of the disciples to the majesty of Jesus.