The feast of the Transfiguration of Christ celebrates the revelation of Christ’s divine glory on Mount Tabor in Galilee (Matthew 17:1-6; Mark 9:1-8; Luke 9:28-36). After revealing to His disciples that He would be put to death in Jerusalem (Matthew 16:21), Christ, along with Ss. Peter, James, and John, went up the mountain. There, St. Matthew writes, “he was transfigured before them. And his face did shine as the sun: and his garments became white as snow.”
The brightness was not something added to Christ but the manifestation of His true divine nature. For Peter, James, and John, it was also a glimpse of the glories of heaven and of the resurrected body promised to all Christians. As Christ was transfigured, two others appeared with Him: Moses, representing the Old Testament Law, and Elijah, representing the prophets. Thus Christ, Who stood between the two and spoke with them, appeared to the disciples as the fulfillment of both the Law and the prophets.
At Christ’s baptism in the Jordan, the voice of God the Father was heard to proclaim that “This is my beloved Son” (Matthew 3:17). During the Transfiguration, God the Father pronounced the same words (Matthew 17:5).
Despite the importance of this event, the Feast of the Transfiguration was not among the earliest of the Christian feasts. It was celebrated in Asia starting in the fourth or fifth century and spread throughout the Christian East in the centuries following. The Catholic Encyclopedia notes that it wasn’t commonly celebrated in the West until the tenth century. To celebrate the great Christian victory at the Siege of Belgrade in 1456, during which the Muslim Turks were routed and the Islamic advance into Europe was halted, Pope Callixtus III elevated the Transfiguration to a feast of the universal Church and established August 6 as the date of its celebration