Jesus had taken the three up to the mountain with Him to pray, and as He prayed, two Old Testament prophets suddenly appeared side by side with Jesus, Who was transformed right before the apostles' eyes.
What issue of vital importance did Jesus, Moses and Elijah discuss during this power encounter? We read the Gospel of Luke to find out (italics mine for emphasis):
28 About eight days after these words, He took along Peter, John, and James and went up on the mountain to pray.
29 As He was praying, the appearance of His face changed, and His clothes became dazzling white.
30 Suddenly, two men were talking with Him—Moses and Elijah.
31 They appeared in glory and were speaking of His death, which He was about to accomplish in Jerusalem.
In Matthew 17, we read:
9 As they were coming down from the mountain, Jesus commanded them, “Don’t tell anyone about the vision until the Son of Man is raised from the dead.”
and in Mark 9:
9 As they were coming down from the mountain, He ordered them to tell no one what they had seen until the Son of Man had risen from the dead.
10 They kept this word to themselves, discussing what “rising from the dead” meant.
The two prophets confirmed before the three apostles what Jesus had been telling them all along, but which the apostles still would not understand until after it had all happened. Jesus had taught them, as He teaches us today, that He had come to earth to die a horrifyingly cruel death on a cross to save us from our sins and prove to us His very name, Yeshua: "the Lord saves."
In all three of these Gospels, the Father speaks from heaven and confirms to them once again that Jesus is His Beloved Son, in Whom He delights.
By speaking from heaven at that precise moment, the Father confirmed that He had sent the Son on this mission.
By raising Jesus from the dead, the Father confirmed that the mission had been a roaring success: the veil in the Temple was torn in two, the Perfect Sacrifice had been made, our access to the Father restored by the Son.
Jesus is Lord!
Painting: "The Transfiguration" by Carl Heinrich Bloch
Was Jesus Crucified?
EyeWitness Report... The Crucifixion