Commemorated on August 6 / 19
According to Bishop Nikolai Velimirovch in The Prologue from Ohrid:
In the third year of His ministry, the Lord Jesus spoke more frequently to His disciples of His coming Passion, but linked it always with His glory after His suffering on the Cross. That His coming suffering should not utterly shatter His disciples, so that they fall away from Him, He, the all-Wise, decided to show them, before His Passion, something of His divine glory. He therefore, taking with Him Peter, James and John, went by night onto Mount Tabor and was there transfigured before them. `And His face shone as the sun, and His raiment became white as snow`, and there appeared beside Him Moses and Elias, the great prophets of the Old Testament. And the disciples saw and were amazed, and Peter said: `Lord, it is good for us to be here; if Thou wilt, let us make here three tabernacles: one for Thee, one for Moses and one for Elias.` While Peter was still speaking, Moses and Elias disappeared and a bright cloud came and overshadowed the Lord and the disciples, and a voice came out of the cloud: `This is My beloved Son, in whom I am well pleased; hear ye Him.` Hearing this voice, the disciples fell prostrate on the ground as though dead, and remained thus lying in fear until the Lord came to them and said: `Arise, and be not afraid` (Matt. 17).
Why did the Lord take only three disciples with Him onto Tabor, and not all of them? Because Judas was not worthy to behold the divine glory of the Master whom he was to betray, and the Lord did not want to leave him alone at the foot of the mountain, that the betrayer should not thus work his betrayal. Why was He transfigured on the mountain and not in the valley? That He might teach us two virtues: love of toil and pondering on God. To climb to the heights involves toil, and the heights represent the heights of our thoughts: pondering on God. Why was He transfigured at night? Because the night is more fitted to prayer and meditation than the day, and because the night covers all earthly beauty with darkness and reveals the beauty of the starry heavens. Why did Moses and Elias a pear? To shatter the Jewish fallacy that Christ was one of the prophets - Elias, Jeremiah or one of the others. This was why He revealed Himself as King over the prophets, and why Moses and Elias appeared as His servants. Up to this moment, the Lord had many times shown His divine power to His disciples, but on Tabor He showed them His divine nature. This vision of His divinity and the hearing of the heavenly witness to Him as the Son of God must have been of support to the disciples in the days of the Lord`s suffering, for the strengthening of a steadfast faith in Him and His final victory.