In commenting on Luke 9:32 on this Feast of the Transfiguration of Our Lord, Saint Ambrose of Milan writes:
”Peter saw this grace, and so did those who were with him, although they were heavy with sleep. The incomprehensible magnificence of the Godhead overwhelms the perceptions of our body. If the sharpness of bodily vision cannot bear the ray of the sun directly into watching eyes, how may the corruption of human members endure the glory of God? The garment of the body, purer and finer after the removal of the materiality of vices, is made for the resurrection. Perhaps they were so heavy with sleep that they saw the radiance of the resurrection after their rest. Keeping vigil, they saw his majesty, because no one sees the glory of Christ unless he is vigilant (Exposition of the Gospel of Luke, 7).”