Jesus clearly calls this mysterious occurrence a "vision" (verse 9). It was not reality but a glimpse of what the future held for Jesus Christ.
The word "transfigured" in verse 2 sounds esoteric, but it is merely the passive form of the Greek word metamorphoo, meaning "changed in form" or "transformed." This same word is used in the well-known Romans 12:2, ". . . be transformed by the renewing of your mind. . . ." Unlike Matthew and Mark, Luke uses the phrase egeneto heteron, translated as "was altered" and meaning "became different" (Luke 9:29). In the vision, the three disciples saw Jesus change to the form He will have in God's Kingdom, which He alluded to in Matthew 16:28.
Why did Moses and Elijah appear with Him? This is where the events of Matthew 16 become important. These two servants of God were the most revered among all the Old Testament figures. Moses, the Great Lawgiver, personified the Law, and Elijah, the Archetypal Prophet, the Prophets. Evidently, the vision depicted Moses and Elijah speaking to Jesus in a servant-Master relationship, but the disciples failed to see this vital distinction.
Notice how Peter puts it. "Let's make three tabernacles, one for each of you." The other accounts say he did not really know what he was saying, meaning that he had missed something in his fear, that he spoke without thinking it through (Mark 9:6; Luke 9:33).
What happened as a result of his thoughtless comment? Notice that Matthew writes, "While he was still speaking. . . ." This is a big clue. God, immediately seeing that the disciples did not understand, took steps to make it plain. To paraphrase what God says, "Look! Jesus is MY beloved Son, and He has MY highest approval. Listen to what HE says! He is far greater than Moses and Elijah, the Law and the Prophets."
This is why the transfiguration occurred. God wanted to make it very clear to the disciples that His way of life is based on the life and death and life again of Jesus Christ, not on the Jews' traditional beliefs. He had to stun the disciples so that they would put Jesus and His teachings on a higher level than Judaism—even higher than the teachings of Moses and Elijah.
Whatever Jesus says is far more important to our salvation than the minutiae of Moses' law or the vagaries of prophecy. In many instances, Jesus makes upgrades to Old Testament law, giving a higher, spiritual meaning (for instance, Matthew 5:21-22). Hear Him!
Richard T. Ritenbaugh
Why the Transfiguration?
When Peter recollected in II Peter 1:16, he was recalling the event in Matthew 17. When Jesus was transfigured, glorified before them, He did not take on a different shape and form than He had before. He still had a recognizable face. He still had clothing on, but everything became shining and bright. Undoubtedly, this was done to impress on the minds of these three men that this Jesus was God in the flesh.
John W. Ritenbaugh
Image and Likeness of God (Part 2)
Simple logic tells us that this was the voice of God the Father. It could not have been an angel, or the words would be a lie!
Although we can accept these gospel accounts as accurate records of what happened, Matthew, Mark, and Luke were not present during the transfiguration. For a firsthand account we must look to Peter, who, along with James and John, was actually there:
For we did not follow cunningly devised fables when we made known to you the power and coming of our Lord Jesus Christ, but were eyewitnesses of His majesty. For He received from God the Father honor and glory when such a voice came to Him from the Excellent Glory: "This is My beloved Son, in whom I am well pleased." And we heard this voice which came from heaven when we were with Him on the holy mountain. (II Peter 1:16-18)
Although Peter wrote these words around AD 66 or 67—almost forty years after the transfiguration occurred—his excitement about the experience was not dampened at all. But what did he, James, and John see, a glorified Jesus conversing with the ghosts of Moses and Elijah? No. What they saw was a vision of the future. They saw a vision of Jesus Christ in His glorified state in His Kingdom along with two of His resurrected servants, Moses and Elijah.
And what did the three amazed disciples hear? They heard the voice "from the Excellent Glory" (some translations render this phrase "the voice of majestic glory," or better, "the voice of supreme glory"). This was not the voice of an angel but that of God the Father! Was it really the Father's voice? Yes, this was the voice of supreme glory, a title that can apply only to the Sovereign God the Father. As stated before, since the voice refers to Jesus as "My Son," it must have been Jesus' heavenly Father speaking.
The Voice of God
Other Forerunner Commentary entries containing Matthew 17:5: