He tried to grasp the meaning of some of the things the priest was doing before the altar. But the man turned his back to the people the whole time, and they could not possibly hear a word of what he was whispering while he moved about up there, doing things. And by degrees, as Paul discovered that the service must be in full swing, and the deep silence prevailed in the empty, sun-lit church, and the few people in the seats continued to kneel as though lost in self-contemplation, he felt a kind of thrill. Why yes, this was beautiful in its way; he suddenly though he understood what people meant when they spoke of the invisible God—he could imagine that priest and congregation were gathered together here to worship something invisible. This form of service could not possibly have any other meaning, for there was nothing here of the priest turning to the congregation and concerning himself with them; it was as though this man took the lead in conducting some worship or other. And for the first time in his life he thought he could perceive some sense in divine service—in this silent adoration he could imagine that a Being was present to receive their souls.
—from The Wild Orchid by Sigrid Undset, Ch. 5
—Cardinal Robert Sarah, from this May 23, 2016 interview
To convert is to turn towards God. I am profoundly convinced that our bodies must participate in this conversion. The best way is certainly to celebrate — priests and faithful — turned together in the same direction: toward the Lord who comes. It isn’t, as one hears sometimes, to celebrate with the back turned toward the faithful or facing them. That isn’t the problem. It’s to turn together toward the apse, which symbolizes the East, where the cross of the risen Lord is enthroned.
By this manner of celebrating, we experience, even in our bodies, the primacy of God and of adoration. We understand that the liturgy is first our participation at the perfect sacrifice of the cross. I have personally had this experience: In celebrating thus, with the priest at its head, the assembly is almost physically drawn up by the mystery of the cross at the moment of the elevation.
Thus, to celebrate facing the people became a possibility, but not an obligation. The Liturgy of the Word justifies the face-to-face [orientation] of the lector and the listeners, the dialogue and the teaching between the priest and his people. But from the moment that we begin to address God — starting with the Offertory — it is essential that the priest and the faithful turn together toward the East. This corresponds completely with that which was willed by the Council Fathers.