Mark 9:2

(Hom. in Matt. 65) Luke in saying, After eight days, does not contradict this; for he reckoned in both the day on which Christ had spoken what goes before, and the day on which he took them up. And the reason that he took them up after six days, was that they might be filled with a more eager desire during the space of these days, and with a watchful and anxious mind attend to what they saw.

(Vict. Ant. e Cat. in Marc.) He does not however show His glory in a house, but He takes them up into a high mountain, for the loftiness of the mountain was adapted to showing forth the loftiness of His glory.

(in Marc. 3, 37) Our Saviour then when transfigured did not lose the substance of real flesh, but showed forth the glory of His own or of our future resurrection; for such as He then appeared to the Apostles, He will after the judgment appear to all His elect. It goes on, And his raiment became shining.

And He takes with Him the three chiefs of the Apostles, Peter, as confessing and loving him, John, as the beloved one, James, as being sublime in speech and as a divine; for so displeasing was he to the Jews, that Herod wishing to please the Jews slew him. And He took them apart, because He was about to reveal mysteries to them. We must also understand by transfiguration not the change of His features, but that, whilst His features remained as before, there was added unto Him a certain ineffable brightness. Again mystically; after the end of this world, which was made in six days, Jesus will take us up (if we be His disciples) into an high mountain, that is, into heaven, where we shall see His exceeding glory.

After the consummation of the cross, the glory of the resurrection is shown, that they, who were to see with their own eyes the glory of the resurrection to come, might not fear the shame of the cross; wherefore it is said, And after six days Jesus taketh with him Peter, and James, and John, and led them up into an high mountain apart by themselves, and he was transfigured before them.