The transfiguration is the miraculous manifestation of Jesus' glory along with the glorified forms of Moses and Elijah (Matthew 17:1 - 9, Mark 9:1 - 10, Luke 9:27 - 36). This manifestation was witnessed by three specially selected disciples (Peter, James and John) who were on a high mountain with the Lord when the event took place.
The Bible reveals that Moses and Elijah, during the transfiguration, were discussing with Jesus his upcoming suffering and death in Jerusalem (Luke 9:31). Christ himself had only first begun to openly teach the details of his upcoming sacrifice to his disciples less than two weeks prior (Matthew 16:21, Mark 8:31).
As the three men were speaking, a cloud enveloped them with the voice of God declaring, "This is My Son, the Beloved. Listen to Him!" (Luke 9:35, HBFV throughout). The cloud, along with Moses and Elijah, then quickly disappeared.
Was it real?
The Lord, when the transfiguration ended, revealed to his three disciples what they had experienced along with a stern warning, "Tell the VISION to no one until the Son of man has risen from the dead" (Matthew 17:9).
Visions are like the dreams humans experience while sleeping except they take place when a person is wide-awake! Like dreams, a vision can be quite detailed and seem real. They both, however, only take place inside our minds and not in reality.
Where did it take place?
Jesus and his disciples were in Caesarea Philippi (Matthew 16:13, Mark 8:27) six days before his transfiguration took place (Matthew 17:1, Mark 9:2). He then decided to take three of the disciples to an unspecified high mountain where he would pray (Luke 9:28).
At a straight-line distance of only 15 miles (24.1 kilometers) to the northeast, the likely candidate for this high mountain is Mount Hermon (or one of its peaks). The majestic peaks of Hermon marked the northernmost territory God gave the Israelites as a land inheritance (Deuteronomy 3:8, Joshua 11:17, 1Chronicles 5:23).
When did it occur?
Jesus' statements about his upcoming betrayal and death (Matthew 17:22 - 23, Luke 9:43 - 44) places the transfiguration in 29 A.D., the year before his crucifixion. John's gospel also reveals this year's Feast of Tabernacles, celebrated in October, was fast approaching (John 7:2). This explains why Peter wanted to build booths on the mountain (Leviticus 23:39 - 43, Matthew 17:4).
This display of glory almost certainly took place in September. In fact, given its prophetic symbolism, it highly likely occurred on the Feast of Trumpets in 29 A.D., which began at sunset on Monday, September 26 (Harmony of the Gospels by F. Coulter).
Surprisingly, the transfiguration also likely took place after sunset! Luke states the three disciples were "heavy with sleep" while Jesus prayed (Luke 9:32). It is only when they suddenly awoke that they witnessed the vision. Christ was known for frequently praying at night (Matthew 14:23, 26:36, Luke 6:12, etc.).
What does it mean?
There are manifold meanings attached to the transfiguration. Some of these include the following.
1) It reinforced, especially given God's words (Luke 9:35) and what Elijah and Moses were perceived to discuss, that Jesus' teachings fortelling his suffering and death would surely happen.
2) The appearance of Moses, symbolizing God's law and Elijah, representing the prophets, testified how both the law and the prophets (Matthew 11:13, Luke 24:44, John 1:45) prophesied about Jesus' coming, ministry, death and resurrection.
3) The transfiguration revealed the glory Jesus possessed as a member of the Godhead, the same glory he will display at his Second Coming! His prophetic return, possibly starting on the Feast of Trumpets, will be as King of Kings (Revelation 19:16) to bring God's righteous Kingdom to the earth (Luke 9:27).
4) The transfiguration vision revealed the glory the resurrected saints will possess in the first resurrection that takes place during the return of Jesus.