Ambrose of Milan
Catena Aurea · Lukasevangelium 9
But Peter and they that were with him were heavy with sleep: and when they were awake, they saw his glory, and the two men that stood with him. And it came to pass, as they departed from him, Peter said unto Jesus, Master, it is good for us to be here: and let us make three tabernacles; one for thee, and one for Moses, and one for Elias: not knowing what he said. While he thus spake, there came a cloud, and overshadowed them: and they feared as they entered into the cloud. And there came a voice out of the cloud, saying, This is my beloved Son: hear him. And when the voice was past, Jesus was found alone. And they kept it close, and told no man in those days any of those things which they had seen.
For the incomprehensible brightness of the Divine nature oppresses our bodily senses. For if the sight of the body is unable to contain the sun’s ray when opposite to the eyes which behold it, how can the corruption of our fleshly members endure the glory of God? And perhaps they were oppressed with sleep, that after their rest they might behold the sight of the resurrection. Therefore when they were awake they saw His glory. For no one, except he is watching, sees the glory of Christ. Peter was delighted, and as the allurements of this world enticed him not, was carried away by the glory of the resurrection. Hence it follows, And it came to pass as they departed, &c.