Origen
Catena Aurea · Matthäusevangelium 17
While he yet spake, behold, a bright cloud overshadowed them: and behold a voice out of the cloud, which said, This is my beloved Son, in whom I am well pleased; hear ye him. And when the disciples heard it, they fell on their face, and were sore afraid. And Jesus came and touched them, and said, Arise, and be not afraid. And when they had lifted up their eyes, they saw no man, save Jesus only. And as they came down from the mountain, Jesus charged them, saying, Tell the vision to no man, until the Son of man be risen again from the dead.
The bright cloud overshadowing the Saints is the Power of the Father, or perhaps the Holy Spirit; or I may also venture to call the Saviour that bright cloud which overshadows the Gospel, the Law, and the Prophets, as they understand who can behold His light in all these three.