27 For I saw a light from heaven that excelled the sun, and its light shone upon me. So then mighty rays streamed forth without moderation, and were poured upon feeble eyes, which moderate rays refresh. For, lo! The sun also in measure assists the eyes, but beyond measure and out of measure it injures the eyes. And it is not by way of vengeance in wrath that it smites them. For lo! It is the friend of the eyes and beloved of the eyeballs. And this is a marvel; while with its gentle lustre it befriends and assists the eyes; yet by its vehement rays it is hostile to and injures the eyeballs.
But if the sun which is here below, and of kindred nature with the eyes that are here below, yet injures them, in vehemence and not in anger, in its proper force and not in wrath; how much more should the light that is from above, akin to the things that are above, by its vehemence injure a man here below who has suddenly gazed upon that which is not akin to his nature? For since Paul might have been injured by the vehemence of this sun to which he was accustomed, if he gazed upon it not according to custom, how much more should he be injured by the glory of that light to which his eyes never had been accustomed?
For behold, Daniel also was melted and poured out on every side before the glory of the angel, whose vehement brightness suddenly shone upon him! And it was not because of the angel's wrath that his human weakness was melted, just as it is not on account of the wrath or hostility of fire that wax is melted before it; but on account of the weakness of the wax it cannot keep firm and stand in presence of fire. When then the two approach one another, the power of the fire by its quality prevails; but the weakness of the wax on the other hand is brought lower even than its former weakness.
Source: On Our Lord (New Advent)