Take a moment to consider some of the great events of this mystery. Jesus, Whom the Apostles have seen live the life of a man and all that comes with it, except sin, see Him in resplendent light. Even His clothing is whiter than any white has ever been (Mark 9:2)! Then, they see Moses and Elijah conversing with Him. They who symbolize the Law and the Prophets (i.e. the core of the Jewish faith), are converging on Christ. As if that was not enough, God the Father spoke to them those beautiful words, "This is my beloved Son, in Whom I am well pleased, listen to Him." (Matthew 17:5)
After all of this - the glory, the amazement, the fear (proper fear of the Lord); Peter, James, and John fell the ground. Then, Jesus came and touched them and said, "Arise and fear not." (Matthew 17:7). The Second Person of the Blessed Trinity, the God-man, touched His Apostles and encouraged them. How beautifully tender.
May this Feast of the Transfiguration be blessed and holy for you all!