In the eastern apse of the great basilica, one sees the incomparable mosaic of the Transfiguration, and of the revelations of God to the Prophet Moses. This work dates to the sixth century, and was completed shortly after the construction of the basilica. Christ is depicted in the centre, his face shining like the sun, and his garments as white as light. Moses and Elias stand, speaking with him, while the Apostles Peter, James, and John are prostrate, overcome with the dazzling brightness of the revelation.

Medallions depicting the apostles are ranged above, and medallions depicting the prophets are ranged below. These depictions include two historical figures, Longinus the Abbot, and John the Deacon.

Above the depiction of the Transfiguration, there are depictions of Moses at the Burning Bush (on the top left), and Moses receiving the tablets of the Law (on the top right). The area below shows two angels flying towards the center, holding orbs and sceptres surmounted with crosses. They offer these to Christ the Lamb, depicted in a central medallion. Two other medallions comprise a Deeisis: the Virgin Mary to the right, and Saint John the Forerunner to the left. This is referred to as the Deeisis, or Entreaty, in that the All-holy Virgin and the Forerunner intercede before Christ.

The apse of the Chapel of the Burning Bush contains a simple mosaic, with a geometrical cross set into a gold ground. Fragments of mosaic discovered during archaeological digs at the peak of Sinai show that the sixth century basilica built there was also adorned with mosaics.