Christ was transfigured before Peter, James, and John to strengthen them with the hope of the Resurrection so that they would not despair at the Passion. The Transfiguration is a lesson to teach the Apostles that "the Christ must suffer and so enter into his glory."
Likewise, the Church gives us this Gospel on the Second Sunday of Lent to strengthen us with the hope of Easter so that we might persevere in accomplishing our Lenten discipline. We also learn that each Christian must suffer (through voluntary penance) in order to enter into the glory of the Risen Lord.
Moses and Elijah appear with Jesus - It is striking to note that these are the only other two men in Sacred Scripture who fasted for forty days. If we want to have a joy-filled and holy Easter, it is necessary that we enter into these forty days of penance and fasting with the Lord.
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