John Chrysostom — as excerpted in the Catena Aurea on John 6:15-21

“(Hom. xliii. 1) And at last He appears quite unexpectedly: They see Jesus walking upon the sea, drawing nigh. He reappears after His retirement, teaching them what it is to be forsaken, and stirring them to greater love; His reappearance manifesting His power. They were disturbed, were afraid, it is said. Our Lord comforts them: But He saith unto them, It is I, be not afraid.”