Ante-Nicene Fathers, Vol IX:
Origen's Commentary on the Gospel of Matthew.: Chapter XXXVIII

38.  The Garments White as the Light.

And not only is He transfigured before such disciples, nor does He only add to the transfiguration the shining of His face as the sun; but further also to those who were led up by Him into the high mountain apart, His garments appear white as the light. 5784   But the garments of Jesus are the expressions and letters of the Gospels with which He invested Himself.  But I think that even the words in the Apostles which indicate the truths concerning Him are garments of Jesus, which become white to those who go up into the high mountain along with Jesus.  But since there are differences also of things white, His garments become white as the brightest and purest of all white things; and that is light.  When therefore you see any one not only with a thorough understanding of the theology concerning Jesus, but also making clear every expression of the Gospels, do not hesitate to say that to Him the garments of Jesus have become white as the light.  But when the Son of God in His transfiguration is so understood and beheld, that His face is a sun, and His garments white as the light, straightway there will appear to him who beholds Jesus in such form Moses,—the law—and Elijah,—in the way of synecdoche, not one prophet only, but all the prophets—holding converse with Jesus; for such is the force of the words “talking with Him;” 5785 but, according to Luke, “Moses and Elijah appeared in glory,” down to the words, “in Jerusalem.” 5786   But if any one sees the glory of Moses, having understood the spiritual law as a discourse in harmony with Jesus, and the wisdom in the prophets which is hidden in a mystery, 5787 he sees Moses and Elijah in glory when he sees them with Jesus.

Footnotes

Matt. xvii. 2.

Matt. xvii. 3.

Luke 9:30, 31.

1 Cor. ii. 7.