And after six days Jesus taketh unto him Peter and James, and John his brother, and bringeth them up into a high mountain apart: And he was transfigured before them. And his face did shine as the sun: and his garments became white as snow. And behold there appeared to them Moses and Elias talking with him. And Peter answering, said to Jesus: "Lord, it is good for us to be here: if thou wilt, let us make here three tabernacles, one for thee, and one for Moses, and one for Elias." And as he was yet speaking, behold a bright cloud overshadowed them. And lo a voice out of the cloud, saying: "This is my beloved Son, in whom I am well pleased: hear ye him." And the disciples hearing fell upon their face, and were very much afraid. And Jesus came and touched them: and said to them: "Arise, and fear not." And they lifting up their eyes, saw no one, but only Jesus. And as they came down from the mountain, Jesus charged them, saying: "Tell the vision to no man, till the Son of man be risen from the dead." (Matt. 17:1-9)
THE DIVINITY OF CHRIST IS PROVED:
a) by the testimony of His heavenly Father, Who, at the time of our Lord's Transfiguration, declared for the second time that Jesus was His beloved Son.
b) by the teaching of the apostles, who were eye-witnesses of His divine glory. This glory was visibly manifested at the Transfiguration, and was seen by the three apostles. Therefore St. Peter was able to write in his second epistle (I:16, 17, 18) thirty-five years later: "For we have not followed cunningly devised fables, when we made known to you the power and presence of our Lord Jesus Christ: but having been made eye-witnesses of His majesty. For He received from God the Father honor and glory; this voice coming down to Him from excellent glory: 'This is My beloved Son in whom I have pleased Myself. Hear ye Him!' And this voice we heard brought from heaven, when we were with Him in the holy mount."
c) by our Lord's own prophecy of His Resurrection, when He forbade the apostles to tell what they had seen, till after He had risen from the dead.
[From 'A Practical Commentary on Holy Scripture' by Bishop Knecht, D.D.]
(1899 Douay-Rheims Bible)