Some interesting thoughts on the Transfiguration over at JoyfulChristian, particularly on the role of John as 'Elijah', and why there was to be an Elijah figure to precede the Messiah.
Moses and Elijah appeared on the mount and spoke with Jesus. What were they talking about? Luke records, they 'were speaking of His departure, which He was about to accomplish at Jerusalem.' (10:32) Jesus stood transfigured before the selected apostles--they viewed Him as He truly was. And Peter--not realizing what he was saying (how typical of Peter--and us!)--offered to build tents (or tabernacles) for Moses, Elijah and Jesus. God was not satisfied with Peter's solution: 'This is My Son, My Chosen One; listen to Him!' (vs. 35) It was now time for authority to reside in the Person of Jesus Christ (Heb. 1:1-2), not the Law (Moses) and the Prophets (Elijah). The old wineskins would no longer suffice.