Luke 9:29

Or else, according to your capacity is the word either lessened or increased to you, and unless you ascend the summit of a higher wisdom, you behold not what glory there is in the word of God. Now the garments of the Word, are the discourses of the Scriptures, and certain clothings of the Divine mind; and as His raiment shone white, so in the eyes of your understanding, the sense of the divine words becomes clear. Hence after Moses, Elias; that is, the Law and the Prophets in the Word. For neither can the Law exist without the Word, nor the Prophet, unless he prophesied of the Son of God.

Now the transfigured Saviour shows the glory of His own coming, or our resurrection; who as He then appeared to His Apostles shall in like manner appear to all the elect. But the raiment of the Lord is taken for the band of His Saints, which in truth when our Lord was upon earth seemed to be despised, but when He sought the mount, shines with a new whiteness; for now are we the sons of God; and it does not yet appear what we shall be. But we know that, when he shall appear, we shall be like him. (1 John 3:2.)

(ut sup. 13.) Now the devil, seeing His face shining in prayer, recollected Moses, whose face was glorified. But Moses indeed was arrayed with a glory, which came from without; our Lord, with that which proceeded from the inherent brightness of Divine glory. (Exod. 34:29.) For since in the hypostatical union there is one and the same glory of the Word and the flesh, He is transfigured not as receiving what He was not, but manifesting to His disciples, what He was. Hence, according to Matthew, it is said, that He was transfigured before them, and that His face shone as the sun; (Mat. 17:2.) for what the sun is in things of sense, God is in spiritual things. And as the sun, which is the fountain of light, cannot be easily seen, but its light is perceived from that which reaches the earth; so the countenance of Christ shines more intensely, like the sun, but His raiment is white as snow; as it follows, And his raiment was white and glistering; that is, lighted up by its participation of the divine light.

Or, Peter went up, who received the keys of the kingdom of heaven; John, to whom was committed our Lord's mother; James, who first suffered martyrdom. (Acts 12:1.) Now in a mystical manner, after the words above said, is exhibited the transfiguration of Christ, since he who hears the words of Christ, and believes, shall see the glory of His resurrection. For, on the eighth day the resurrection took place. Hence also several Psalms are written, 'for the eighth,' (pro octava.) or perhaps it was that He might make manifest what He had said, that he who for the word of God shall lose his own life, shall save it, seeing that He will make good His promises at the resurrection. But Matthew and Mark have related that He took them with Him after six days, of which we may say after 6000 years, (for a thousand years in the Lord's sight are as one day;) but more than 6000 years are reckoned. We had rather then take the six days symbolically, that in six days the works of the world were completed, that by the time we may understand the works, by the works the world. And so the times of the world being finished, the resurrection to come is declared; or because, He who has ascended above the world, and has passed beyond the moments of this life, is waiting, seated as it were on a high place, for the everlasting fruit of the resurrection. I should think that in the three who are taken up into the mountain, was contained in a mystery the human race, because from the three sons of Noah sprung the whole race of man; I did not perceive that they were chosen out. Three then are chosen to ascend the mountain, because none can see the glory of the resurrection, but they who have preserved the mystery of the Trinity with inviolable purity of faith.

Not as though His body changed its human form, but a certain glistening glory overspread it.