This feast is the anniversary of the death of Pope Paul VI (1978). I was a novice at the time. Pope Paul had the difficult task of leading the Church during the chaotic period right after Vatican II.
In the Gospel for today's feast, Jesus goes up the mountain with Peter, James, and John. While he is transfigured in glory, Moses and Elijah appear. Jesus speaks with them about his coming Passion and death. Moses and Elijah represent the Law and the Prophets. Jesus brings both of those to fulfillment.