St. Nikolai Velimirovich
In the third year of His preaching, the Lord Jesus often spoke to His disciples of His approaching passion but at the same time of His glory following His suffering on the Cross. So that His impending passion would not totally weaken His disciples and that no one would fall away from Him, He, the All-wise, wanted to partially show them His divine glory before His passion. For that reason, He took Peter, James and John with Him and, with them, went out at night to Mt. Tabor and there was transfigured before them: "And His face shone as the sun and His garments became white as snow" (Matthew 17:2). There appeared along side Him, Moses and Elijah, the great Old Testament prophets. And, seeing this, His disciples were amazed. Peter said: "Lord, it is good for us to be here: if You will, let us make here three tabernacles; one for You, one for Moses and one for Elijah" (Matthew 17:4). While Peter still spoke, Moses and Elijah departed and a bright cloud overshadowed the Lord and His disciples and there came a voice from the cloud saying: "This is my beloved Son in whom I am well pleased; hear Him" (Matthew 17:5). Hearing the voice, the disciples fell to the ground on their faces as though dead and remained that way, lying in fear, until the Lord came near to them and said: "Arise and be not afraid" (Matthew 17:7).
Why did the Lord take only three disciples on Tabor and not all? Because Judas was not worthy to behold the divine glory of the Teacher, Whom he will betray and the Lord did not want to leave him [Judas] alone at the foot of the mountain so that the betrayer would not, by that, justify his betrayal.
Why was our Lord transfigured on a mountain and not in a valley? So as to teach us two virtues: love of labor and godly-thoughts. For, climbing to the heights required labor and height represents the heights of our thoughts, i.e., godly-thoughts.
Why was our Lord transfigured at night? Because, the night rather than the day is more suitable for prayer and godly-thoughts and because the night, by its darkness, conceals all the beauty of the earth and reveals the beauty of the starry heavens.
Why did Moses and Elijah appear? In order to destroy the error of the Jews, as though Christ is one of the prophets; Elijah or Jeremiah or some other that is why He appears as a King above the prophets and that is why Moses and Elijah appear as His servants. Until then, our Lord manifested His divine power many times to the disciples but, on Mt. Tabor, He manifested His divine nature. This vision of His Divinity and the hearing of the heavenly witness about Him as the Son of God, should serve the disciples in the days of the Lord's passion, in strengthening of an unwavering faith in Him and His final victory.
Why did our Lord not manifest His divine glory on Tabor before all the disciples instead of before three of them? First, because He Himself gave the Law through the mouth of Moses: "At the mouth of two witnesses or at the mouth of three witnesses, shall the matter be established" (Deuteronomy 19:15). Therefore, three witnesses are sufficient. These three witnesses represent three main virtues: Peter Faith, for he was the first to confess his faith in Christ as the Son of God; James Hope, for, with faith in the promise of Christ, he was the first who laid down his life for the Lord, being the first to be slain by the Jews; John Love, for he reclined on the bosom of the Lord and remained beneath the Cross of the Lord until the end. God is not called the God of many but rather the God of the chosen. "I am the God of Abraham, the God of Isaac and the God of Jacob" (Exodus 3:6). God often valued a faithful man more than an entire nation. Thus, on many occasions, He wanted to destroy the entire Jewish nation, but because of the prayers of righteous Moses, spared that nation to live. God listened more to the faithful Prophet Elijah than to the entire unbelieving kingdom of Ahab. Because of the prayers of one man, God towns and people. Thus, the sinful town of Ustiug was to be destroyed by fire and hail had it not been saved by the prayers of the one and only righteous man in it, St. Procopius, the "fool for Christ" (July 8).