37 Nor are the Gospels silent concerning the glory of His present reigning body. It is written that the Lord said, Verily, I say unto you, there be some of them that stand here, which shall not taste of death till they see the Son of Man coming in His Kingdom. And it came to pass, after six days Jesus takes with Him Peter and James and John His brother, and brings them up into a high mountain apart. And Jesus was transfigured before them, and His face did shine as the sun, and His garments became as snow. Thus was shown to the Apostles the glory of the body of Christ coming into His Kingdom: for in the fashion of His glorious Transfiguration, the Lord stood revealed in the splendour of His reigning body.
Source: On the Trinity (New Advent)