There are two possible “points” or focuses for the Mass: God or the People of God. In ad orientem celebration of Mass the priest is not so much “turning his back to the people” as he is facing the same way as his people and praying with them. Together their orientation is away from themselves and towards God. The “point,” therefore, is to turn our hearts to the Lord.
It seems obvious that God should be at the center of our worship, and Cardinal Sarah explains that the liturgy “is the door to our union with God. If Eucharistic celebrations turn into human self-celebrations, there is a great danger, because God disappears. We have to start by placing God back at the center of the liturgy. If the man is the center, the Church becomes a merely human society, a simple NGO.”
At the heart of the Christian experience is repentance and conversion of life. The word metanoia or repentance actually means “turning in a new direction.” Therefore, at Mass when we orient ourselves toward the tabernacle, toward the Lord’s presence, we are turning in a new direction—turning away from ourselves and toward him.
The idea of the priest turning his full attention to the act of worship isn’t really bad. It’s kind of a comforting thought. It might give Mass a more reverent feeling, too.
[UPDATE July 5th, 2016: Cardinal Robert Sarah, the Vatican’s liturgy chief, has asked priests to begin celebrating Mass ad orientem at advent, it seemed prudent to bring this poll back for a second round.]