Jesus did many extraordinary things while on earth as a human. One such extraordinary event that occurred was Jesus meeting with the supposed long-dead Elijah and Moses. This episode explains the reason for this meeting and its significance to all believers. Interestingly, Jesus selected Peter, James, and John to accompany him to view His transfiguration
“And he was transfigured before them, and his face shone like the sun, and his clothes became white as light. And behold, there appeared to them Moses and Elijah, talking with him.” Matthew 17:2-3, Mark 9:2-3 & Luke 28:28-29
Jesus had already shared with the disciples His mission on Earth, that he had to die but then He would be raised to life but the disciples did not understand the full extent of what God and Jesus were accomplishing for mankind.
The fact that Jesus was transfigured before them confirmed His heavenly origins, as well the appearance in a glorified state of Moses and Elijah who had been dead thousands of years confirmed life after death. It is interesting that Peter, James and John knew who Moses and Elijah were without Jesus having to introduce them. Hence this event and its timing was important in the progression of Jesus revealing who He was and His mission on Earth.