The Transfiguration is a Gospel event from the life of Jesus that is reported in three of the four gospels (Matthew 17:1-9, Mark 9:2-8, Luke 9:28-36). Jesus went up a mountain with his disciples that overlooks Jerusalem and is seen with Elijah and Moses while he “transfigures”, meaning that the disciples see Jesus as He would appear after the resurrection. The gospels report that Jesus face and clothes became “dazzling white.”
The story is meant to not simply be a miracle but also has several other meanings to ponder. One is that Jesus is the fulfillment of the old law and the prophets (why He is seen with Moses (Giver of the law) and Elijah (greatest of all prophets). As they overlook Jerusalem the story foreshadows where this fulfillment of the law will take place: Jerusalem–where Jesus will meet his death.
The disciples are confused by the event and don’t realize that Jesus must die in order to save the world.
Lastly, the story is a foretaste of what is in store for us. We will all rise again and Jesus gives his disciples just a glimpse of what the afterlife holds for both them and us.