By St. John of Damascus
A bright cloud overshadowed them, and seeing within it Jesus the Savior with Moses and Elijah, the disciples were filled with great fear.
Of old when Moses saw God he experienced the divine darkness, indicating the symbolic nature of the law; for as Paul has written, the law contained only a shadow of the things to come, not the reality itself. In the past Israel could not look at the transient glory on the face of Moses; but we, beholding the glory of the Lord with unveiled faces, are being transformed from one degree of glory to another by the Lord who is the Spirit. The cloud, therefore, that overshadowed the disciples was not one of threatening darkness but of light; for the mystery hidden from past ages has been revealed to show us perpetual and eternal glory. Moses and Elijah, representing the law and the prophets, stood by the Savior because he whom the law and the prophets proclaimed was present in Jesus, the giver of life.
And a voice from the cloud said: 'This is my beloved Son with whom I am well pleased; listen to him.'
The voice of the Father came from the cloud of the Spirit: 'This is my beloved Son.' He who is seen in human form, who became man only yesterday, who lives humbly in the midst of us, and whose face is now shining, is he who is. 'This is my beloved Son, the eternal, the only begotten of the only God, he who proceeds timelessly and eternally from me, his Father; who did not begin to exist after me, but is from me and with me and in me from all eternity.'
It was by the Father's good pleasure that his only begotten Son and Word became incarnate; it was by the Father's good pleasure that the salvation of the world was achieved through his only begotten Son; it was the Father's good pleasure which brought about the union of the whole universe in his only begotten Son. For humanity is a microcosm linking in itself all visible and invisible being, sharing as it does in the nature of both, and so it must surely have pleased the Lord, the creator and ruler of the universe, for divinity and humanity and thus all creation to be united in his only begotten and consubstantial Son, so that God might be all in all.
'This is my Son, the radiance of my glory, who bears the stamp of my own nature, through whom I created the angels, through whom the vault of heaven was made firm and the earth established. He upholds the universe by his powerful word, and by the Spirit which proceeds from his mouth, that is the life-giving and guiding Spirit. Listen to him. Whoever receives him, receives me who sent him by the authority not of a stern master but of a father. As a man he is sent, but as God he abides in me and I in him. Whoever refuses to honor my only begotten Son refuses to honor me, his Father who sent him. Listen to him, for he has the words of eternal life.'
From a homily by Saint John of Damascus on the Transfiguration, PG 96, 572-573.