Upon Mount Tabor, Jesus revealed to his disciples a heavenly mystery. While living among them he had spoken of the kingdom and of his second coming in glory, but to banish from their hearts any possible doubt concerning the kingdom and to confirm their faith in what lay in the future by its prefiguration in the present, he gave them on Mount Tabor a wonderful vision of his glory, a foreshadowing of the kingdom of heaven. It was as if he said to them: “As time goes by you may be in danger of losing your faith. To save you from this I tell you now that some standing here listening to me will not taste death until they have seen the Son of Man coming in the glory of his Father.” Moreover, in order to assure us that Christ could command such power when he wished, the evangelist continues: Six days later, Jesus took with him Peter, James and John, and led them up a high mountain where they were alone. There, before their eyes, he was transfigured. His face shone like the sun, and his clothes became as white as light. Then the disciples saw Moses and Elijah appear, and they were talking to Jesus.
From a sermon on the transfiguration of the Lord by Saint Anastasius of Sinai, bishop