About the power of the Divine Spirit, through Whom the Kingdom of God is to be revealed, the Lord predicted: “There are some standing here who shall not taste death, until they have seen the Son of Man coming in His Kingdom” (Mt 16:28). Everywhere and in every way the King will be present, and everywhere will be His Kingdom, since the advent of His Kingdom does not signify the passing over from one place to another, but rather the revelation of its power of the Divine Spirit. That is why it is said: “come in power.” And this power is not manifest to simply ordinary people, but to those standing with the Lord, that is to say, those who have affirmed their faith in Him like Peter, James and John, and especially those who are free of our natural abasement. Therefore, and precisely because of this, God manifests Himself upon the Mount, on the one hand coming down from His heights, and on the other, raising us up from the depths of abasement, since the Transcendent One takes on mortal nature. Certainly, such a manifest appearance by far transcends the utmost limits of the mind’s grasp, as effectualized by the power of the Divine Spirit.
Thus, the Light of the Transfiguration of the Lord is not something that comes to be and then vanishes, nor is it subject to the sensory faculties, although it was contemplated by corporeal eyes for a short while upon an inconsequential mountaintop. But the initiates of the Mystery, (the disciples) of the Lord at this time passed beyond mere flesh into spirit through a transformation of their senses, effectualized within them by the Spirit, and in such a way that they beheld what, and to what extent, the Divine Spirit had wrought blessedness in them to behold the Ineffable Light.
Those not grasping this point have conjectured that the chosen from among the Apostles beheld the Light of the Transfiguration of the Lord by a sensual and creaturely faculty, and through this they attempt to reduce to a creaturely level not only this Light, the Kingdom and the Glory of God, but also the Power of the Divine Spirit, through Whom it is meet for Divine Mysteries to be revealed. In all likelihood, such persons have not heeded the words of the Apostle Paul: “Eye has not seen, nor ear heard, nor has it entered into the heart of man, what things God has prepared for those who love Him. But to us God has revealed them through His Spirit. For the Spirit searches all things, even the deep things of God” (1 Cor 2:9-10). …
Even the face of Moses was illumined by his association with God. Do you not know that Moses was transfigured when he went up the mountain, and there beheld the Glory of God? But he (Moses) did not effect this, but rather he underwent a transfiguration. However, our Lord Jesus Christ possessed that Light Himself. In this regard, actually, He did not need prayer for His flesh to radiate with the Divine Light; it was but to show from whence that Light descends upon the saints of God, and how to contemplate it. For it is written that even the saints “will shine forth like the sun” (Mt 13:43), which is to say, entirely permeated by Divine Light as they gaze upon Christ, divinely and inexpressibly shining forth His Radiance, issuing from His Divine Nature. On Mount Tabor it was manifest also in His Flesh, by reason of the Hypostatic Union (i.e., the union of the two perfect natures, divine and human, within the divine Person [Hypostasis] of Christ, the Second Person of the Most Holy Trinity). The Fourth Ecumenical Council at Chalcedon defined this Hypostatic union of Christ’s two natures, divine and human, as “without mingling, without change, without division, without separation.”
We believe that at the Transfiguration He manifested not some other sort of light, but only that which was concealed beneath His fleshly exterior. This Light was the Light of the Divine Nature, and as such, it was Uncreated and Divine. So also, in the teachings of the Fathers, Jesus Christ was transfigured on the Mount, not taking upon Himself something new nor being changed into something new, nor something which formerly He did not possess. Rather, it was to show His disciples that which He already was, opening their eyes and bringing them from blindness to sight. For do you not see that eyes that can perceive natural things would be blind to this Light?
Thus, this Light is not a light of the senses, and those contemplating it do not simply see with sensual eyes, but rather they are changed by the power of the Divine Spirit. They were transformed, and only in this way did they see the transformation taking place amidst the very assumption of our perishability, with the deification through union with the Word of God in place of this.
St Gregory Palamas