St. Gregory on the Transfiguration
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?
from a Sermon on the Transfiguration
St. Gregory Palamas, Archbishop of Thessalonica, +1359