The icon of the Transfiguration portrays Christ surrounded by the glorious light of his divinity and clothed in the same garments in which he is depicted in all representations of the Resurrection. To his left is Moses, holding the Tablets of the Law, while to his right is shown the Prophet Elias.
St. John Chrysostom offers various reasons for the appearance of these particular Old Testament figures at the Transfiguration. They represent the Law and the Prophets. Both had visions of God. Moses represent the dead while Elias, having been carried up to heaven in a chariot of fire, represents the living, over whom both the living and the dead, Christ reigns in glory. 1
1 Come Bless The Lord, GOD WITH US, Catechetical Series, 1976.