Ecce Vir Oriens nomen ejus

"Behold a Man, the Orient is His Name..." (3rd antiphon at Vespers of Christ the King).

In the Coptic Liturgy, directly before the Sursum corda dialogue that leads into the Preface, or rather into the whole Eucharistic Prayer or ‘Anaphora’, the deacon (or, in his absence, the server) exclaims: “Stand up with fear and trembling! Look toward the east and say: ‘Mercy, peace, and sacrifice of praise!’”. This is expressed in Greek as Εἰς νατολὰς βλέψατε, and in Latin as Aspicite ad orientem – a phrase founded upon Baruch 4:36 and 5:5. 

The Coptic admonition states explicitly what all liturgies assume: that worship is directed toward the (liturgical) east. For the east, synonymous with the dawn and with the sun, is a symbol of Christ, who is the Orient, toward Whom all should turn: the true East (cf. Zech 6:12, LXX & Vulg.), the dawn from on high (Lk 1:78), the sun of justice (Mal 4:2a (or 3:20a)), the true light of the world (Jn 8:12; 9:5), Who has risen and Who shall never set, Who has ascended above the heaven of heavens to the east, and ought be hymned as God in that direction (Ps 67(68):33, Vulg.), Who shall come again in glory as lightning flashing from the east to the west (Mt 24:27), as was prophesied by Ezekiel (43:2).

Augustine says (De Verbis Domini, Sermone 100,2): “The East,” that is Christ, “calleth thee, and thou turnest to the West,” namely mortal and fallible man. 

(St Thomas Aquinas, S.T.,IIaIIæ,189,10, resp.)

[what a woe for the Church, then, to have fallen from her age-old orientation!]

You entered, then, [into the baptistery] in order to encounter your adversary [the devil], whom you were determined to renounce to his face [facing west]; then you turned to the east, for he who renounces the devil turns to Christ, and looks him straight in the face. 

(St Ambrose, On the Mysteries, 7)

The catechumen, standing with his face to the West, which symbolized the abode of darkness, and stretching out his hand, or sometimes spitting out in defiance and abhorrence of the devil [the so-called sputatio], was wont to make this abjuration. It was also customary after this for the candidate for baptism to make an explicit promise of obedience to Christ. This was called by the Greeks syntassesthai Christo, the giving of oneself over to the control of Christ. St. Justin Martyr testifies that baptism was only administered by those who, together with their profession of faith, made a promise or vow that they would live in conformity with the Christian code. Hence the generally employed formula: syntassomai soi, Christe, "I surrender myself to thee, O Christ, to be ruled by thy precepts". This [syntaxis] took place directly over the apotaxis or renunciation of the devil, and was variously described by the Latins as promissum, pactum, and votum. During this declaration of attachment to Jesus Christ the person to be baptized turned towards the East as towards the region of light. 

(Delany, Joseph F. “Baptismal Vows,” Catholic Encylopedia, vol. II, 1907)

The Christian churches are turned toward the East, in order that our gaze may be directed toward the paradise, our ancient fatherland, from which we have been chased away. And we pray Our Lord to re-entrust us to this place from which we were chased away. 

(Pseudo-Athanasius)

It is from the East that comes salvation; from there comes that man called Orient, mediator between God and men. 

(Origen, Homil. IX in Lev. n. 10)

[The rising sun is an image of the Risen Christ] for that sun which seems to be dying in the West, we see it resurrect with such glory in the East. 

(Honorius of Autun)

The Lord himself says to us: ‘In the same way lightning leaves from the East to the West, so will it be for the coming of the Lord’; and it is for the very fact that we await his coming that we pray in the direction of the East. 

(St John Damascene)

There is a certain fittingness in adoring towards the east. First, because the Divine majesty is indicated in the movement of the heavens which is from the east. Secondly, because Paradise was situated in the east according to the Septuagint version of Genesis 2:8, and so we signify our desire to return to Paradise. Thirdly, on account of Christ Who is “the light of the world” (Jn 8:12; 9:5), and is called “the Orient” (Zech 6:12), “Who mounteth above the heaven of heavens to the east” (Ps 67(68):33), and is expected to come from the east, according to Matthew 24:27, “As lightning cometh out of the east, and appeareth even into the west; so shall also the coming of the Son of Man be.”  

(St Thomas Aquinas, S.T.,IIaIIæ,84,3, resp. ad obj. 3)

This worshipping, or adoration in Churches was not so indefinite, but that it was instantly limited to be towards the East, or the place of the Altar, insomuch that amongst the first blossomes of Heresyes, that of the Osseni [Elchasaites] as reckoned by Epiphanius, of whom Alxai [Elchasai] the false Jew was a Coryphæus, prohibit enim (saith the father) orare ad orientes, asserens non oportere sic intendere, saying we ought not addresse our devotions, or adorations that way. That was his hæresy; for that thither our adorations are to be directed is an Apostolicall tradition, if we will believe as authentick records, as any we have extant. Justin Martyr in Resp. ad Qu: 118 ad Orthodoxos, having sayd that the Church hath received order for the place, and manner of prayer from the Apostles (as S. Clement sayd we had from Christ) addes, ideo Christianos omnes precum tempore spectare ad Orientem: quia ortus tamquam mundi pars honoratior, adorationi Dei destinatus est. Marke that; the East is the determin’d place for adoration: and this by the practise of all Christians, and this taught from the Apostles. The certainty of this derivation from the Apostles is further to be seen in Origen Homil. 5. in Numer: in Tertullian cap. 16 Apologet: S. Gregory Nyssen in lib. de Oratione: Athanasius Quæst:14. de plurimus et necessariis quæst: and divers others.

The reasons of this determination of Christian worship are diversly given by the Fathers according to their various Conceptions, all thereof, or the most were postnate to the thing, and are to be seene in S. German’s Theorica rerum Ecclesiast: and Damascen: lib. 4. orthod: fid: cap. 13. where he sayes this addresse of our adoration is studiose observanda, Christum scil: cum in cruce penderet ad occasum prospexisse, eumque nomine ita adoramus, ut eum obtueamur. The true reason I know not, I meane that which was truly introductive of the practise, for postnate there are enough, but this I know, that our adoration thitherward, and the placing of the Altar there were coætaneous for ought appears, and if I may have leave to conjecture, I think that this was the truer reason of the addresse of our worship, even because the Altar was Positum in Oriente; my reason is this;

1. Because I find in antiquity προσκυνειν προς άνατολας [‘to worship toward the east’], and έμπροσθεν του θυσιαστηριου [‘in front of the altar’] used promiscuously, and, 2ndly, because I find in antiquity the prærogative of holinesse not given to the orientall part of heaven, but to the site of the Altar in the Church I doe: which two things put together methinks say, that therefore the adoration was alwayes that way, because the Altar or Holy Table (for the difference is but nominall) being alwayes like the tree of Paradise planted in the East, and being more Holy than the other parts of the Church, I meane by a relative holinesse, did best determine our worship, as having God there the most presentiall. And if I be not mistaken, Walafridus Strabus shall confirme it; for when he had reckoned three Altars, one at Jerusalem, one in the Pantheon at Rome, the other in S. Peters that were not set in the East as examples of singular exception from the Common rule addes, Usus tamen frequentior et rationi vicinior habet in Orientem Orantes converti. Though these Altars were not in the East, yet the most common use is for worshippers to turne to the East when they pray. As if their addresse to the East was onely because of the Altar’s being there placed.  

(an extract from: Jeremy Taylor, On the Reverence due to the Altar.)