Augustine of Hippo

But how could they understand this, except from His going a different way, wishing to pass them as strangers; for they were so far from recognising Him, as to take Him for a spirit. For it goes on: But when they saw him walking upon the sea, they supposed it had been a spirit, and cried out. (ubi sup.) How then could He wish to pass them, whose fears He so reassures, if it were not that His wish to pass them would wring from them that cry, which called for His help?

Catena Aurea by Aquinas ↗

Gregory the Dialogist

It can also be asked why, when the disciples were laboring on the sea, the Lord stood on the shore after His resurrection, though before His resurrection He had walked on the waves of the sea before His disciples. The reason for this matter is quickly understood if the cause that was then present is considered. For what does the sea signify except the present age, which dashes itself against the tumults of affairs and the waves of corruptible life? What is figured by the solidity of the shore except that perpetuity of eternal rest? …

Forty Gospel Homilies, Homily 24 ↗

Bede

And he wanted to pass them by. But when they saw him walking on the sea, they thought he was a ghost, and they cried out. For they all saw him and were troubled. Even now heretics think the Lord was a ghost and did not truly take on flesh from the virgin. Indeed, Theodore of Pharan, once a bishop, wrote that the Lord did not have physical weight according to the flesh but walked on the sea without weight and body. …

On the Gospel of Mark ↗