John Chrysostom

"And he said, Come. And when Peter was come down out of the ship, he walked on the water, and came to Jesus. But when he saw the wind boisterous, he was afraid; and beginning to sink, he cried, saying, Lord, save me. And immediately Jesus stretched forth His hand and caught him, and saith unto him, O thou of little faith, wherefore didst thou doubt?" This is more wonderful than the former. Therefore this is done after that. For when He had shown that He rules the sea, then He carries on the sign to what is yet more marvellous. …

Homily on the Gospel of Matthew 50 ↗

Theophylact of Ohrid

The Lord laid the sea down beneath Peter's feet, revealing His power. See how Peter prevailed over that which was greater, the sea, but was afraid of the lesser peril, the wind; such is the weakness of human nature. And it was as soon as he became afraid that he began to sink. For when his faith weakened, then Peter went down. The Lord did this so that Peter would not become puffed up, and to console the other disciples who perhaps envied him. Whereupon Christ also showed how much greater He was than Peter.

Commentary on Matthew ↗

Augustine of Hippo

For in one Apostle, namely Peter, first and chief in the order of Apostles in whom was figured the Church, both kinds were to be signified; that is, the strong, in his walking upon the waters; the weak, in that he doubted, for to each of us our lusts are as a tempest. Dost thou love God? Thou walkest on the sea; the fear of this world is under thy feet. Dost thou love the world? It swallows thee up. But when thy heart is tossed with desire, then that thou mayest overcome thy lust, call upon the divine person of Christ.

Catena Aurea by Aquinas ↗

Jerome

Let those who think that the Lord's body was not real, because He walked upon the yielding waters as a light æthereal substance, answer here how Peter walked, whom they by no means deny to be man.

Catena Aurea by Aquinas ↗

Thomas Aquinas

Then the sign is presented; hence he said come. And Peter going down out of the boat, walked upon the water to come to Jesus. And this is against the Manicheans who said that Christ did not have a true body; because if Christ did not have one because he walked upon the waters, neither did Peter. By the fact that after the fourth watch danger still threatened, it is signified that in the fourth coming, whatever needs to be purified in the elect will be purified. Ps. …

Commentary on Matthew ↗