What does Matthew 17:3 mean?

Jesus has been transfigured: described using the word from which we get the term metamorphosis. This transformation occurred before the eyes of Peter, James, and John (Matthew 17:1–2). He is radiating the glory of God as light, and His clothes have become intensely white. He stands on top of the mountain changed into a more-native appearance as the Son of God in heaven.

To further confirm that the disciples are glimpsing the glory of heaven, Moses and Elijah appear on the mountain, as well, and begin talking with Jesus. The fact that these two heroes of Judaism appear is significant. For one, it confirms that there is a life after death where they continue to dwell. Many scholars suggest that the pair are also meant to represent the Law and the Prophets that are so central to God's relationship with Israel. God gave the Law to Moses to the give to the people, and Elijah was the most notable of all the prophets that followed. In addition, both men interacted with God on Mount Sinai, later called Mount Horeb (Exodus 24:15–16; 1 Kings 19:8).

Jesus has come to fulfill the Law and the prophecies about the Messiah (Matthew 5:17–18). He does not stand equal with this pair, but above them as the Son of God. The fact that the three are talking indicates that Jesus knows both men personally. Luke's account mentions that they talked about Jesus' "departure," meaning His death, which was to happen soon in Jerusalem (Luke 9:31). Moses and Elijah are shown to be aware of the plans of heaven for the completion of Jesus' mission on earth.