Origen

“ But perhaps the voice from the cloud says to Moses and Elijah, “This is My beloved Son in whom I am well-pleased, hear Him,” as they were desirous to see the Son of man, and to hear Him, and to behold Him as He was in glory. ”

“ For since it is the function of a tabernacle to overshadow him who is in it, and to shelter him, and the bright cloud overshadowed them, God made, as it were, a diviner tabernacle, inasmuch as it was bright, that it might be to them a pattern of the resurrection to come; for a bright cloud overshadows the just, who are at once protected and illuminated and shone upon by it. ”