19 So when they had rowed about five and twenty or thirty furlongs, they see Jesus walking on the sea, and drawing nigh unto the ship: and they were afraid.
[AD 407] John Chrysostom on John 6:15-21
(Hom. xlii. 3) See what the belly can do. They care no more for the violation of the Sabbath; all their zeal for God is fled, now that their bellies are filled: Christ has become a Prophet, and they wish to enthrone Him as king. But Christ makes His escape; to teach us to despise the dignities of the world. He dismisses His disciples, and goes up into the mountain.— (Hom. xliii. 1). These, when their Master had left them, went down in the evening to the sea; as we read; And when even was now come, His disciples went down unto the sea. They waited till evening, thinking He would come to them; and then, as He did not come, delayed no longer searching for Him, but in the ardour of love, entered into a ship, and went over the sea toward Capernaum. They went to Capernaum thinking they should find Him there.

(Hom. xlii. 1) The mention of the time is not accidental, but meant to show the strength of their love. They did not mate excuses, and say, It is evening now, and night is coming on, but in the warmth of their love went into the ship. And now many things alarm them: the time, And it was now dark; and the weather, as we read next, And the sea arose by reason of a great wind that blew; their distance from land, So when they had rowed about five and twenty or thirty furlongs.

(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.

(Hom. xliii. s. 1) He appeared to them in this way, to show His power; for He immediately calmed the tempest: Then they wished to receive Him into the ship; and immediately the ship was at the land, whither they went. So great was the calm, He did not even enter the ship, in order to work a greater miracle, and to show his Divinity more clearlyg.

(Hom. xliii. 1) Jesus does not show Himself to the crowd walking on the sea, such a miracle being too much for them to hear. Nor even to the disciples did He show Himself long, but disappeared immeditately.

(Hom. xliii. 1) Or take another explanation. This miracle seems to me to be a different one, from the one given in Matthew: for there they do not receive Him into the ship immediately, whereas here they doh: and there the storm lasts for some time, whereas here as soon as He speaks, there is a calm. He often repeats the same miracle in order to impress it on men's minds.

[AD 735] Bede on John 6:15-21
The multitude concluding, from so great a miracle, that He was merciful and powerful, wished to make Him a king. For men like having a merciful king to rule over them, and a powerful one to protect them. Our Lord knowing this, retired to the mountain: When Jesus therefore perceived that they would come and take Him by force to make Him a king, He departed again into a mountain Himself alone. From this we gather, that our Lord went down from the mountain before, where He was sitting with His disciples, when He saw the multitude coming, and had fed them on the plain below. For how could He go up to the mountain again, unless He had come down from it.

(in v. cap. Joan.) The way of speaking we use, when we are in doubt; about five and twenty, we say, or thirty.

(in Matt. c. xiv.) He does not say, I am Jesus, but only I am. He trusts to their easily recognising a voice, which was so familiar to them, or, as is more probable, He shows that He was the same who said to Moses, I am that I am (Exod. 3:14)

This ship, however, does not carry an idle crew; they are all stout rowers; i. e. in the Church not the idle and effeminate, but the strenuous and persevering in good works, attain to the harbour of everlasting salvation.

[AD 804] Alcuin of York on John 6:15-21
Baskets are used for servile work. The baskets here are the Apostles and their followers, who, though despised in this present life, are within filled with the riches of spiritual sacraments. The Apostles too are represented as baskets, because, that through them, the doctrine of the Trinity was to be preached in the four parts of the world. His not making new loaves, but multiplying what there were, means that He did not reject the Old Testament, but only developed and explained it.

[AD 1107] Theophylact of Ohrid on John 6:15-21
Observe the three miracles here; the first, His walking on the sea; the second, His stilling the waves; the third, His putting them immediately on shore, which they were some distance off, when our Lord appeared.

When either men or devils try to terrify us, let us hear Christ saying, It is I, be not afraid, i. e. I am ever near you, God unchangeable, immoveable; let not any false fears destroy your faith in Me. Observe too our Lord did not come when the danger was beginning, but when it was ending. He suffers us to remain in the midst of dangers and tribulations, that we may be proved thereby, and flee for succour to Him Who is able to give us deliverance when we least expect it. When man's understanding can no longer help him, then the Divine deliverance comes. If we are willing also to receive Christ into the ship, i. e. to live in our hearts, we shall find ourselves immediately in the place, where we wish to be, i. e. heaven.

[AD 407] John Chrysostom on John 6:19
And, lastly, by reason of the strangeness of the thing, for,

They see Him walking upon the sea. And when they were greatly troubled,
[AD 444] Cyril of Alexandria on John 6:19-20
Christ does not appear to those in the boat immediately after they set sail or at the onset of danger but only when they are far away from the shore. For the grace of our Savior does not come to us when our tribulations begin but when our fear is at its height and the danger shows itself to be great—when we are found, so to say, in the midst of the waves of affliction. Then, Christ appears unexpectedly and removes our fear and frees us from all danger. By his ineffable power he changes horror into joy, and as it were, calms the storm.… When Christ appears and looks on us, we shall effortlessly succeed even against our hope. And we who are in danger because of our distance from Christ shall no longer have to labor to accomplish what is helpful for us when he is present. Christ is our deliverance from all danger and the accomplishment of achievements beyond hope to those who receive him.

[AD 735] Bede on John 6:19-20
He says only “I am.” He trusts that they will easily recognize his voice, which was so familiar to them. Or, more probably, he shows that he was the same who said to Moses, “Say to the children of Israel, the one who is has sent me to you.”