John Chrysostom

And wherefore are the disciples troubled, being poor, yea, exceedingly poor? Wherefore then are they confounded? Being in pain about the salvation of the rest, and having a great affection for all, and having already taken upon themselves the tender bowels of teachers. They were at least in such trembling and fear for the whole world from this declaration, as to need much comfort.

Homily on the Gospel of Matthew 63 ↗

Theophylact of Ohrid

When His disciples heard it, they were exceedingly amazed, saying, Who then can be saved? But Jesus beheld them, and said unto them, With men this is impossible: but with God all things are possible. The disciples, being compassionate, did not ask this question for their own sake, for they were poor, but for all men. The Lord therefore teaches us not to gauge salvation by human weakness, but by God's power. …

Commentary on Matthew ↗

Augustine of Hippo

Whereas the rich are few in comparison of the multitude of the poor, we must suppose that the disciples understood all who wish for riches, as included in the number of the rich.

Catena Aurea by Aquinas ↗

Thomas Aquinas

And when they had heard these things, the disciples wondered very much, saying: who then can be saved? Above the Lord assigned the reason for his doctrine; here he responds to the astonishment of the disciples. And first the astonishment is presented; secondly the satisfaction, at and Jesus beholding, said to them. He says therefore and when they had heard these things, the disciples wondered very much, saying: who then can be saved? But here there is a literal question. …

Commentary on Matthew ↗