Now, you will most often hear this posture referred to as, "the priest with his back to the people." Well, that's accurate to some degree but unhelpful. How often do we refer to us having our backs to each other? Even in "churches in the round," a good number of people sit with their backs to people behind them; yet no one seems to think this is somehow a slight from one to the other; and the reason is because we are concerned with what we're turned toward--i.e., toward the Lord. So why is it that we all understand the need for everyone in church to be turned toward the Lord...except for the one leading our worship, offering the Sacrifice for us, in our name, with our participation?Father has written an excellent essay which clarifies some aspects of what is happening by intent from the Holy Father. Please read his excellent essay!
Now, some will say, rightly, that we are all focused on the altar; but if we press the point, then we're conceding we want the priest focused on the altar...not the assembly. Is that right? And if that is what we really want, then we've hit on the very reason this issue matters.
Let's begin with an obvious point: the priest, the people, all of us are human; I mean, we're prone to human weakness. So, in our worship, we make allowance for human weakness, human needs, human ways of understanding, and human limitations. In the seminary, this--stated a different way--was called "the Sacramental Principle": God communicates with us in a fashion suited to our needs and limitations.
Well, here's the difficulty: when the people and the priest are facing each other at various points of the Mass, the most natural thing is that we look at each other. That is just plain common sense. On the other hand, it is rather difficult, although not impossible, that people can face each other, and not look...at each other.
So, for example, there are people who watch me purify the vessels at the altar after communion. While it is edifying--if they realize what it means--I don't see why it is something anyone should feel the need to observe; and yet they do, because the priest is "doing something." Something in us is distracted by that. That's just human. I.e., the time of silent prayer, after communion, is probably more reflective if the priest is sitting or kneeling; which, when time is not an issue, I do after the purification. But when the clock is ticking, or a baby is screaming, then I move Mass to a conclusion.