And why do we call it transfiguration? That's the question I’ve asked myself.
As the story went, Jesus took three of his best disciples (Peter, John, James), went to Mt. Hermon and there his countenance turned dazzling white; Moses and Elijah appeared before Him and paid Him homage; and Peter said... well, everyone knows the story .
You also probably know, that the Transfiguration of Jesus, like almost everything else in the New Testament, was preceded by Old Testament events - the transfiguration of Moses. Moses’ countenance irradiated bright light, when he went down from Mount Sinai. “The skin of his face shone because he had been speaking with the Lord.”.
“This is my beloved Son, with whom I am well pleased; listen to him!” 
So why do we call it Transfiguration and not Glorification or, say, Encomium, or, even, Countenance, for this word has a surprisingly matching second meaning? After all, transfiguration literally means a change of shape. I am afraid that the responsibility solely lies on Saint Gerome.
In his c. 400 AD translation of Exodus, when describing Moses returning from Mt. Sinai with the tablets, St. Gerome translated Hebrew “karan 'ohr panav’ i.e. 'facial skin that glowed with rays” into “cornuta esset facies sua” i.e. “his face was horned”. For the details see Dan Brown .
The mistranslation was corrected later , but the term survived. From St. Gerome's part, of course, it was an honest mistake, but it stuck to the Scriptures, like horns to Moses forehead, for over a millennium! Yes, over a thousand years later Michelangelo put horns to Moses head. Think about it:
How would you feel if Michelangelo will make your statue, with a pair of horns attached to your head? That would be a transfiguration indeed Moses could have one big laugh with St. Gerome out there about this mistranslation. I am not sure if Michelangelo would join them, though - it must have been a lot of extra work to do those horns.
In both cases Transfiguration (even without horns) was a terrifying event. Jesus asked his disciples not to be afraid, just as Moses asked his brother and a group Israelites, who were scared to approach him when he returned from Mt. Sinai. (Moses will wear a veil after that event, he will wear it permanently, except for the times when he will be going up the mountain to speak with God) .
St. Peter, who the witnessed Transfiguration of Jesus, confirms his witness in his Second Letter. Please, note what he confirms there :
“For when he received honor and glory from God the father, and the voice was borne to him by the Majestic Glory, ‘This is my beloved Son, with whom I am well pleased,’ we ourselves heard this very voice borne from heaven, for we were with him on the holy mountain.”
Peter talks about the Voice and what it had said, not the dazzling light, etc. In Transfiguration, with horns or without, the key is in the message from the cloud. And hence, we ought to heed His message.
1. Matthew 17:1-13; Mark 9: 2-13: Luke 9:28-36.
2. Exodus 34:27-35.
3. Dan Brown, The Lost Symbol, Anchor Books, New York, 2010, p. 248.
4. 2 Peter 1: 17, 18 Christian Faith and Prayers, Literature, Art, Music, Culture and Nature