Jesus took Peter, James and John up a high mountain to pray.
Jesus was transfigured before them.
"His face became as dazzling as the sun, his clothes as radiant as light."
This was to fortify their faith to withstand the coming tragedy of the Passion.
Jesus foresaw the 'scandal of the cross,' and prepared them for it by this manifestation of His glory.
Moses and Elias (representing the Law and the prophets of the Old Testament) were conversing with Jesus about His passion.
"Do not think I have come to destroy the Law or the Prophets... but to fulfill them."
From a cloud came a voice: "This is my beloved Son, listen to Him."
Jesus admonishes them not to tell the vision to anyone until the Son of Man rises from the dead.
We too will behold the transfigured Jesus on the Last Day.