LITURGY FACING EAST
Ever since ancient times, it has been customary in the prayer of the Eastern Churches to prostrate oneself to the ground, turning toward the east; the buildings themselves were constructed such that the altar would face the east. Saint John of Damascus explains the meaning of this tradition: "It is not for simplicity nor by chance that we pray turned toward the regions of the east (...). Since God is intelligible light (1 Jn. 1:5), and in the Scripture, Christ is called the Sun of justice (Mal. 3:20) and the East (Zech. 3:8 of the LXX), it is necessary to dedicate the east to him in order to render him worship. The Scripture says: 'Then the Lord God planted a garden in Eden, in the east, and he placed there the man whom he had formed' (Gen. 2:8). (...) In search of the ancient homeland and tending toward it, we worship God. Even the tent of Moses had its curtain veil and propitiatory facing the east. And the tribe of Judah, in as much as it was the most notable, encamped on the east side (cf. Nm. 2:3). In the temple of Solomon, the Lord's gate was facing the east (cf. Ez. 44:1). Finally, the Lord placed on the cross looked toward the west, and so we prostrate ourselves in his direction, facing him. When he ascended to heaven, he was raised toward the east, and thus his disciples adored him, and thus he will return, in the same way as they saw him go to heaven (cf. Acts 1:11), as the Lord himself said: 'For just as lightning comes from the east and is seen as far as the west, so will the coming of the Son of Man be' (Mt. 24:27). Waiting for him, we prostrate ourselves toward the east. It is an unwritten tradition, deriving from the Apostles." [St. John of Damascus, <Expositio accurata fidei orthodoxae>]
This rich and fascinating interpretation also explains the reason for which the celebrant who presides in the liturgical celebration prays facing the east, just as the people who participate. It is not a question, as is often claimed, of presiding the celebration with the back turned to the people, but rather of guiding the people in pilgrimage toward the Kingdom, invoked in prayer until the return of the Lord.
-- The paragraphs above are excerpts from the "Instruction for Applying the Liturgical Prescriptions of the Code of Canons of the Eastern Churches" -- 6 Jan. 1996.