The Spirit, too, is light, as we read: “He who has shone in our hearts by the Holy Spirit” (2 Cor. 4:6).
If then the unapproachable is true and this light was unapproachable, the light was not a simulacrum of divinity, but truly the light of the true divinity, not only the divinity of the Son, but that of the Father and the Spirit too.
This is why we sing together to the Lord when we celebrate the annual Feast of the Transfiguration: “In Your light which appeared today on Thabor, we have seen the Father as light and also the Spirit as light,” for “You have unveiled an indistinct ray of Your divinity.”
[…] Denys the Areopagite, Gregory the Theologian and all the others who await His coming from heaven with glory, affirm clearly that Christ will be for all eternity as He then appeared, as we showed above.
This light, then, is not just a phantom without subsistence. Indeed, not only will Christ be eternally thus in the future, but He was such even before He ascended the Mountain.
Hear John Damascene, who is wise in divine things: “Christ is transfigured, not by putting on some quality He did not possess previously, nor by changing into something He never was before, but by revealing to His disciples what He truly was, in opening their eyes and in giving sight to those who were blind.
“For while remaining identical to what He had been before, He appeared to the disciples in His splendour; He is indeed the true light, the radiance of glory.”
Basil the Great testifies to the same truth: “His divine power appeared as it were as a light through a screen of glass, that is to say, through the flesh of the Lord which He had assumed from us; the power which enlightens those who have purified the eyes of the heart.”
And do not the annual hymns of the Church affirm that, even before the Transfiguration, He had previously been such as He then appeared? “What appeared today was hidden by the flesh, and the original beauty, more than resplendent, has been unveiled today.”
Moreover, the transformation of our human nature, its deification and transfiguration—were these not accomplished in Christ from the start, from the moment in which He assumed our nature?
Thus He was divine before, but He bestowed at the time of His Transfiguration a divine power upon the eyes of the apostles and enabled them to look up and see for themselves.
This light, then, was not a hallucination but will remain for eternity, and has existed from the beginning.
Gregory Palamas (1296-1359): The Triads, E 12-15, in Gregory Palamas: The Triads, ed. John Meyendorff, trans. Nicholas Gendle, Classics of Western Spirituality series, Paulist Press, 1983.