Over at Ignatius Insight, there is an excellent article by Carl Olsen where he gives his insights as an Eastern Catholic, as well as, apologetics from Pope Benedict XVI, and Fr. Uwe Michael Lang, in favour of ad orientem.
To help encourage a wide reading of the article, I've posted the full text here:
"When we study the most ancient liturgical practices of the Church we find that the priest and the people faced in the same direction, usually toward the east, in the expectation that when Christ returns, He will return “from the east.” At Mass, the Church keeps vigil, waiting for that return. This single position is called ad orientem, which simply means “toward the east.”
That is from a column by Bishop Edward Slattery of the diocese of Tulsa in the September 2009 issue of The Eastern Oklahoma Catholic (PDF format; ht: New Liturgical Movement), announcing the following:
Even before his election as the successor to St. Peter, Pope Benedict has been urging us to draw upon the ancient liturgical practice of the Church to recover a more authentic Catholic worship. For that reason, I have restored the venerable ad orientem position when I celebrate Mass at the Cathedral. This change ought not to be misconstrued as the Bishop “turning his back on the faithful,” as if I am being inconsiderate or hostile. Such an interpretation misses the point that, by facing in the same direction, the posture of the celebrant and the congregation make explicit the fact that we journey together to God. Priest and people are on this pilgrimage together.
Of course, most Eastern/Byzantine Catholic churches continue to follow and adhere to the ancient practice of ad orientem, as Fr. Uwe Michael Lang notes in Turning Towards the Lord: Orientation in Liturgical Prayer (Ignatius Press, 2009; 2nd edition), pointing out that "the Congregation for the Oriental Churches declared in its instruction Il Padre incomprensibile of 6 January 1996 that the ancient tradition of praying toward the east has a profound liturgical and spiritual value and must be preserved in the Eastern rites" (p. 104). Back in July of 2007, writing about Summorum Pontificum as someone who has been in a Byzantine Catholic parish for ten (now twelve) years, I said:
Having a certain "Eastern" perspective can be helpful. For example, I have to laugh a bit when I read or hear some Catholics insist that having the priest "turn his back to the people" is a bad or bizarre thing, as though it will somehow create a sort of dark and emotionally-draining chasm between the priest and the people. It's interesting to hear the reactions of Western-rite Catholics after they go to Divine Liturgy for the first time; they are usually both mildly confused and extremely moved. And more than once such folks have said, in essence, "Now I understand far better why the priest does that (that is, stands ad orientem)."
Now, after all these years "in the East," whenever I am at a Novus Ordo Mass, I am a bit—maybe even more than a bit—uncomfortable with the priest facing the people (versus populum). Not that my pastor doesn't ever face the people; on the contrary, he faces the people at several different places in the Divine Liturgy, often to bless them, which takes place several times. But during the prayers he faces east with the people. And it not only not bothersome, it makes complete sense, both theologically and liturgically.
Here are a couple of quotes from Cardinal Ratzinger about ad orientem. First, from the third chapter of The Spirit of the Liturgy:
Despite all the variations in practice that have taken place far into the second millennium, one thing has remained clear for the whole of Christendom: praying towards the East is a tradition that goes back to the beginning. Moreover, it is a fundamental expression of the Christian synthesis of cosmos and history, of being rooted in the once-for-all events of salvation history while going out to meet the Lord who is to come again. Here both the fidelity to the gift already bestowed and the dynamism of going forward are given equal expression.
The Orientation of Worship and God’s Omnipresence
Modern man has little understanding of this "orientation." Judaism and Islam, now as in the past, take it for granted that we should pray towards the central place of revelation, to the God who has revealed himself to us, in the manner and in the place in which he revealed himself. By contrast, in the Western world, an abstract way of thinking, which in a certain way is the fruit of Christian influence, has become dominant. God is spiritual, and God is everywhere: does that not mean that prayer is not tied to a particular place or direction?
Now we can indeed pray everywhere, and God is accessible to us everywhere. This idea of the universality of God is a consequence of Christian universality, of the Christian’s looking up to God above all gods, the God who embraces the cosmos and is more intimate to us than we are to ourselves. But our knowledge of this universality is the fruit of revelation: God has shown himself to us. Only for this reason do we know him, only for this reason can we confidently pray to him everywhere. And precisely for this reason is it appropriate, now as in the past, that we should express in Christian prayer our turning to the God who has revealed himself to us. Just as God assumed a body and entered the time and space of this world, so it is appropriate to prayer – at least to communal liturgical prayer – that our speaking to God should be "incarnational," that it should be Christological, turned through the incarnate Word to the Triune God. The cosmic symbol of the rising sun expresses the universality of God above all particular places and yet maintains the concreteness of divine revelation. Our praying is thus inserted into the procession of the nations to God.
On the other hand, a common turning to the East during the Eucharistic Prayer remains essential. This is not a case of something accidental, but of what is essential. Looking at the priest has no importance. What matters is looking together at the Lord. It is not now a question of dialogue, but of common worship, of setting off towards the One who is to come. What corresponds with the reality of what is happening is not the closed circle, but the common movement forward expressed in a common direction for prayer.
And from his Foreword to U.M. Lang's Turning Towards the Lord: Orientation in Liturgical Prayer (2nd edition):
There is nothing in the Council text about turning altars towards the people; that point is raised only in postconciliar instructions. The most important directive is found in paragraph 262 of the Institutio Generalis Missalis Romani, the General Instruction of the new Roman Missal, issued in 1969. That says, 'It is better for the main altar to be constructed away from the wall so that one can easily walk around the altar and celebrate facing the people (versus populum).' The General Instruction of the Missal issued in 2002 retained this text unaltered except for the addition of the subordinate clause, 'which is desirable wherever possible'. This was taken in many quarters as hardening the 1969 text to mean that there was now a general obligation to set up altars facing the people 'wherever possible'.
This interpretation, however, was rejected by the Congregation for Divine Worship on 25 September 2000, when it declared that the word 'expedit' ('is desirable') did not imply an obligation but only made a suggestion. The physical orientation, the Congregation says, must be distinguished from the spiritual. Even if a priest celebrates versus populum, he should always be oriented versus Deum per Iesum Christum (towards God through Jesus Christ). Rites, signs, symbols, and words can never exhaust the inner reality of the mystery of salvation. For this reason the Congregation warns against one-sided and rigid positions in this debate.