They had just seen something no ordinary man could do, and it filled them with a new kind of fear. The storm was over, yet "they feared exceedingly." Their question is wonder, not doubt: who must He be, if creation itself obeys Him? Barnes answers in his note on the calming: "None but the God of the storms and the billows could awe by a word the troubled elements." Gill puts the speakers' conclusion this way: "he must be truly God."

Gill takes the speakers to be "the men in the ship, the mariners to whom the ship belonged," since "the disciples must have known before, who and what he was." Mark simply says "they," and Matthew says "the men marvelled" (Matthew 8:27).

No one in the ship answers the question. Mark's Gospel answers it. Its first line names Him: "Jesus Christ, the Son of God" (Mark 1:1). As soon as they land, a man with an unclean spirit cries out, "Jesus, thou Son of the most high God" (Mark 5:7). Later Peter says, "Thou art the Christ" (Mark 8:29), and at the cross a centurion says, "Truly this man was the Son of God" (Mark 15:39).

"Feared exceedingly" is in Greek ephobēthēsan phobon megan, literally "they feared a great fear." Mark's story moves from "a great storm" (Mark 4:37) to "a great calm" (Mark 4:39) to this great fear, the awe that comes from meeting God's power up close.

"Obey" translates hypakouei. Earlier in Mark, people had said that Jesus commands "even the unclean spirits, and they do obey him" (Mark 1:27). Now the wind and the sea obey Him too.

This is the question at the heart of Mark's Gospel: who is Jesus? The disciples ask it here after He commands the wind and the sea. Barnes describes the scene: "Standing amid the howling tempest, on the heaving sea, and in the darkness of night, by his own power he stills the waves." That is what God does, and Jesus did it by a word.

God reveals the answer step by step. Mark tells the reader from the first line (Mark 1:1), but the disciples learn it along the way, through storms, healings, and finally the cross (Mark 8:29; Mark 15:39). Their fear is not a failure here. It is the right response to discovering who has been sleeping in their boat.