9 But this, that the disciples thought He was a phantom, does not represent these only, does not designate them only who deny that the Lord had human flesh, and who sometimes by their blind perverseness disturb even those who are in the ship; but those also who think that the Lord has in anything spoken falsely, and who do not believe that the things which He has threatened the ungodly will come to pass. As though He were partly true, and partly false, appearing like a phantom in His words, as though He were something which is “yea and nay.”
But they who understand His voice aright, who says, “It is I; be not afraid;” believe at once all the words of the Lord, so that as they hope for the rewards He promises, so do they fear the punishments He threatens. For as that is true which He will say to those who are set on the right hand, “Come, you blessed of My Father, receive the kingdom prepared for you from the foundation of the world;” so is that true, which they on the left hand will hear, “Depart ye into everlasting fire, prepared for the devil and his Angels.” For this very opinion, by which men think that Christ's threatenings against the unrighteous and the abandoned are not true, has arisen from this, that they see many nations and multitudes innumerable subject to His Name; so that hence Christ appears to them to be a phantom, because He walked upon the sea; that is, He seems to speak falsely in His threats of punishment, because, as it were, He cannot destroy such numberless people who are subject to His Name and honour.
But let them hear Him, saying, “It is I;” let them not therefore “be afraid,” who believing Christ to be true in all things, not only seek after what He has promised, but avoid also what He has threatened; because though He walk upon the sea, that is, though all the nations of men in this world are subject unto Him; yet is He no phantom, and therefore He does not speak falsely, when He says, “Not every one that says unto Me, Lord, Lord, shall enter into the kingdom of heaven.”
Source: Sermons on Selected Lessons of the New Testament (New Advent)