Jesus had gone with his disciples Peter, James, and John to Mount Tabor. Christ's appearance was changed while they watched into a glorious radiant figure. There appeared Elijah and Moses, speaking with Jesus. The disciples were amazed and terribly afraid.
This event shows forth the divinity of Christ, so that the disciples would understand after his Ascension that He was truly the radiant splendor of the Father, and that his Passion was voluntary (Mark 9:2-9). It also shows the possibility of our own theosis.
This event was the subject of some debates between Gregory Palamas and Barlaam of Calabria. Barlaam believed that the light shining from Jesus was created light, while Gregory maintained the disciples were given grace to perceive the uncreated light of God. This supported Gregory's larger argument that although we cannot know God in His essence, we can know Him in his energies, as He reveals Himself.
In Greece the harvest season traditionally began on the Transfiguration. Grapes, in particular, were not eaten before August 6. In some parishes, the first grapes would be brought to church for a blessing and distributed to parishioners.
Troparion - Tone 7
You were Transfigured on the Mount, O Christ God, Revealing Your glory to Your disciples as far as they could bear it. Let Your everlasting Light shine upon us sinners! Through the prayers of the Theotokos, O Giver of Light, glory to You!
Kontakion - Tone 7
On the Mountain You were Transfigured, O Christ God, And Your disciples beheld Your glory as far as they could see it; So that when they would behold You crucified, They would understand that Your suffering was voluntary, And would proclaim to the world, That You are truly the Radiance of the Father!
hymns taken from www.oca.org