The Transfiguration of the Lord is an event described in the Nw Testament of the bible, where Jesus is transformed in a god-like shape on a mountain. Apostles Peter, Paul and John were the three witnesses. The mountain might be Mount Tabor in the north of modern Israel, but the scriptures don’t give an exact location.
There he was transfigured before them. His face shone like the sun, and his clothes became as white as the light.
Matthew 17.2 in the New International Version
The event is celebrated an important festival on the Christian calendar on August 6th, by both Western and Eastern Churches. The theological significance of it lies in the apotheosis of Jesus, His changing into God, and in the foreshadowing of the resurrection after his death. Jesus climbs on a mountain to form a connection between heaven and earth, between God and his people.
The Benedictine monks of Chevetogne are specialised in the singing of songs from the Eastern liturgy, and this is no exception. I like those more than the western tradition, as they are more melodic and exciting. Chevetogne was the first choir I heard to sing these, and they are still beautiful.