Theophylact of Ohrid

And he taketh with him Peter, and James, and John. He takes only those who had been witnesses of His glory on Mount Tabor, that they who had seen His glory might also see His sufferings, and learn that He is really man, in that He is sorrowful. And began to be sore amazed, and very heavy. For since He had taken on Himself the whole of human nature, He took also those natural things which belong to man, amazement, heaviness, and sorrow; for men are naturally unwilling to die.

Catena Aurea by Aquinas ↗

Bede

And He takes Peter, and James, and John with Him, and began to be afraid and to be very sorrowful. And He said to them: My soul is sorrowful even unto death. Christ is afraid, while Peter is not afraid. Christ is afraid; Peter says: I will lay down my life for you (John 13). Christ says: My soul is troubled. Both are true, and each is full of reason, because the one who is lower does not fear, and the one who is higher carries the emotion of fear. For he, as a man, does not understand the power of death. …

On the Gospel of Mark ↗

Bonaventure

But who will deliver us from these plagues? Certainly there is one alone who came to deliver us, namely Christ, who made ten condescensions against the ten plagues. The first was down to our flesh. The second was down to our mortality. The third, to our neediness, for he suffered hunger, thirst, and cold. The fourth was to our poverty, for "he was made destitute," having no place to which he might turn. The fifth, to our temptation, when he permitted himself to be tempted; and in this he bore our weakness. …

Collationes de Decem Praeceptis, Collation 7 ↗