Setting and Overview
Matthew usually does not give precise time indications when he is transitioning to a new event or incident in his narrative, and often those are presented in a thematic order that is out of chronological order, so it is surprising at the beginning of chapter 17 to see him give a specific time indication of six days after the preceding event and teaching. It is clear that Matthew (like Mark and Luke) feels that it is important to see the events here as following and connected to the preceding section. Jesus has corrected Peter sharply and warned them about events that are to come, but which the disciples are struggling to accept (16:21-22.) He has also, however, given them a promise regarding his kingdom (16:27-28) and know he will give them a revelation of his glory that should strengthen and encourage them through the trials to come.

Exposition
Jesus takes the inner circle of Peter, James, and John (specified here for the first time but seen earlier in Mark 5:37) up onto a high mountain that is not named in the Gospels (traditionally Mount Tabor, but more likely Hermon or Meron.) When they are alone, he is transfigured and his face shines and his clothes turn impossibly white. This transfiguration brings to mind Moses (Exodus 34:29-35) and he suddenly appears along with Elijah. Moses and Elijah do not often appear together in the Bible or in extrabiblical literature, but the two likely represent the law and the prophets, or more specifically, the beginning and ideal of the prophetic office (Deuteronomy 34:10) and the later prophetic office pointing forward to a messianic future (Malachi 4:4-6.) Peter jumps in with a suggestion to build three shelters, implying a comparable amount of honor for all three men. His misguided suggestion is cut off, however, by a bright cloud (Exodus 13:21-22, 19:9, 24:16, 40:34, I Kings 8:11, Ezekiel 10:18-19, 11:22-24, 43:2-5) and then a voice from heaven declaring Jesus to be God’s unique Son (Matthew 3:17, Isaiah 42:1, Psalm 2:7.) The disciples react to this in terror, but Jesus provides words of comfort and then they see him alone. Moses and Elijah introduced the law and called people to renewed obedience to it respectively, but only Jesus would be able to truly bring the cleansing and transformation necessary for people to truly obey God (Jeremiah 31:33, Hebrews 1:3, II Corinthians 3:18.)
This event has been revelatory for the disciples, but they don’t fully understand everything yet. Furthermore, Jesus warns them against telling the story of the transfiguration until after he is resurrected. The disciples cannot make sense of why Jesus would be raised from the dead, since that would indicate that he would be killed (as he has already predicted.) The experts in the law predicted that Elijah would return before the Messiah and would restore all things (Malachi 4:5-6) and the disciples don’t understand how the Messiah would be killed in such a restored environment. Jesus however explains that John the Baptist fulfilled that prophecy, but that the restoration was not of the same type as the experts in the law predicted. Despite his calls for obedience and repentance, and despite the wide-spread reach and impact of his ministry, there was still much rejection and opposition and John himself had been executed. Therefore, it should not be impossible to accept that Jesus would be killed as well.

Examination and Application
Peter and the other disciples kept thinking that they had a good understanding of what true discipleship to Jesus looked like and that they would be able to be faithful no matter what was coming. They kept discovering, however, that they weren’t as ready as they thought, a pattern that will continue all the way to the Cross (Matthew 26:31-35.) The transfiguration would provide them with assurance and strength, but it wouldn’t come until after they could look back on it with an understanding of Jesus’ crucifixion and resurrection. We too may continually think that we are stronger and more ready than we really are, and so reflecting on and holding onto these passages can provide us with much needed strength and encouragement. Approaching the end of his life, Peter wrote of the transfiguration as proof of Jesus’ glory and reminded his readers of it as necessary and useful for them as they sought to grow in obedience and remain faithful through the trials to come (II Peter 1:3-19.) Such advice remains critical and relevant for us today.