Jesus went up the mountain with Peter, James, and John and was transformed before their eyes. He appeared to them in His glorified humanity and was illumined with the light of divinity. ... Here we have the whole Bible summed up in this one event. The Old Testament, the Law and the Prophets, point to Christ, the eternal Son come in the flesh. Read more. 
This meditation on theosis is appropriate reading for the Great Feast of the Transfiguration, and a sample of the articles available at Discovering Orthodox Christianity , from Antiochian.org and Conciliar Press.