For whoever would save his life will lose it. Jesus begins His ministry with a prayer and ends his ministry with a prayer. Jesus prays while performing miracles. He teaches his disciples to pray. The transfiguration occurs as a prayer experience.
White garments are symbols of joy and celebration.
Moses and Elijah are 2 figures from the Old Testament. Moses was the giver of God's Law, and Elijah was the great prophet through whom God spoke to his people. Their appearance is a sign that the road which Jesus is taking is a fulfillment of the law and the prophets, i.e., a fulfillment of God's will. In the middle of this vision of glory is an image of suffering. Peter wants to make a tent for Jesus.