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

37.  Force of the Words “Before Them.”

But you will ask if, when He was transfigured before those who were led up by Him into the lofty mountain, He appeared to them in the form of God, in which He formerly was, so that He had to those below the form of a servant, but to those who had followed Him after the six days to the lofty mountain, He had not that form, but the form of God.  But hear these things, if you can, at the same time giving heed spiritually, that it is not said simply, “He was transfigured,” but with a certain necessary addition, which Matthew and Mark have recorded; for, according to both, “He was transfigured before them.” 5781   And according to this, indeed, you will say that it is possible for Jesus to be transfigured before some with this transfiguration, but before others at the same time not to be transfigured.  But if you wish to see the transfiguration of Jesus before those who went up into the lofty mountain apart long with Him, behold with me the Jesus in the Gospels, as more simply apprehended, and as one might say, known “according to the flesh,” by those who do not go up, through works and words which are uplifting, to the lofty mountain of wisdom, but known no longer after the flesh, but known in His divinity by means of all the Gospels, and beholden in the form of God according to their knowledge; for before them is Jesus transfigured, and not to any one of those below.  But when He is transfigured, His face also shines as the sun, that He may be manifested to the children of light, who have put off the works of darkness, and put on the armour of light, 5782 and are no longer the children of darkness or night, but have become the sons of day, and walk honestly as in the day; 5783 and being manifested, He will shine unto them not simply as the sun, but as demonstrated to be the sun of righteousness.

Footnotes

Matt. 17:2, Mark 9:2.

Rom. xiii. 12.

Rom. 13:13, 1 Thess. 5:5.