John Chrysostom

"And why doth He occupy the mountain now, and sit there with His disciples?" Because of the miracle which was about to take place. And that the disciples alone went up with Him, was a charge against the multitude which followed Him not. Yet not for this only did He go up into the mountain, but to teach us ever to rest at intervals from the tumults and confusion of common life. For solitude is a thing meet for the study of wisdom. …

Homily on the Gospel of John 42 ↗

Theophylact of Ohrid

He goes up "onto the mountain" because, he says, "they saw the miracles which He performed on the sick." The followers mentioned in Matthew are better and more philosophical, "because they," he says, "were astonished at His teaching, for He taught them as one having authority" (Matt. 7:28, 29). He goes up "onto the mountain" because He was about to perform a miracle. …

Commentary on John ↗

Bede

Our Lord went up to the mountain, when He ascended to heaven, which is signified by the mountain.

Catena Aurea by Aquinas ↗

Thomas Aquinas

Then he gives the location of the miracle, on a mountain; hence he says: Jesus therefore went up a mountain, i.e., privately, and there sat down with his disciples. Now a mountain is a place well suited for refreshment, for according to the Psalm a mountain signifies the perfection of justice: "Your justice is like the mountains of God" (Ps 35:7). …

Commentary on John ↗

Bonaventure

"He went therefore to the mountain." Here is noted the second occasion, namely the suitability of place and time. The place was suitable for performing a miracle, because it was deserted, in which there was a lack of refreshment: therefore He says: "Jesus therefore went to the mountain, and there He sat with His disciples." The place which John calls a mountain on account of its height, Matthew calls a desert on account of its solitude; Matthew 14: "Jesus withdrew by boat to a deserted place apart." And this place was suitable for …

Commentary on John, Chapter 6 ↗