Saint Cosmas the Anchorite calls the Lord's Transfiguration "the revelation" of the mystery hidden before ages." He, along with Saint Anatolios the Hymnographer, observed that the Light of the Transfiguration necessarily prefigures the Resurrection. Not without reason did the Lord charge His disciples, "Tell the vision to no one until the Son of Man be risen from the dead" (Matthew 17:9). The Transfiguration and the Resurrection are connected surely on account of the Uncreated Light, that is, the salvation of the universe involves both moments. To be resurrected "on the last day" is also to enjoy the Light of Divinity. After the Second Coming and the general resurrection of all flesh, the creation will enter into perfect union with God Who will be "all in all" (Ephesians 1:23)
Of course, those who will be "partakers of the Divine Nature" are members of the Church, the resurrected and transfigured Body of Christ. The presence of Moses and Elias as well as the disciples (later, Apostles) -- Peter, James and John -- all are the foundations of the new Israel. As branches share in the life of their vine, so will those ("branches") engrafted into Christ ("vine") enjoy the light of the eternal God. Hence, the words of the first Kathisma of Matins for the Feast of the Transfiguration,
"Thou hast been transfigured, O Saviour, on Mount Tabor, indicating the transformation of mankind which will occur at Thy dreadful Second Coming, Moses and Elias did converse with Thee. But Thy disciples, Whom Thou didst call, when they beheld Thy Glory, O Master, were dazzled by Thy brightness. Wherefore, O Thou Who didst cause Thy Light to shine on them, enlighten our souls."
Father Michael Azkoul, The Teachings of the Holy Orthodox Church,a book published with the blessing of His Grace, ALYPY, Bishop of Cleveland, and Vicae of Chicago, Detroit and Middle America (ROCOR)