Adam Clarke on Matthew 14:33

Thou art the Son of God - It is probable that these words were spoken either by the sailors or passengers, and not by the disciples. Critics have remarked that, when this phrase is used to denominate the Messiah, both the articles are used, ἑ υιος του Θεου, and that the words without the articles mean, in the common Jewish phrase, a Divine person. It would have been a strange thing indeed, if the disciples, after all the miracles they had seen Jesus work - after their having left all to follow him, etc., were only now persuaded that he was the promised Messiah. That they had not as yet clear conceptions concerning his kingdom, is evident enough; but that they had any doubts concerning his being the promised Messiah is far from being clear.