There's a controversy brewing in the Catholic Church over whether priests should celebrate Mass "facing the people," as the vast majority of them do nowadays (versum populum), or ad orientem, "towards the East," or, colloquially, with his back to the people.

I would guess that most Catholics today have no idea that this back-to-the-people position is an option, and would be sincerely baffled as to why anybody might find it desirable.

And yet, some do. Cardinal Sarah, who heads a Vatican task force on liturgy, recently recommended to priests at a liturgy conference that they start using the ad orientem posture more (and received a standing ovation). Sarah has become the unofficial leader of the loyal traditionalist opposition to Pope Francis, who is widely seen as leading the church in a progressive direction, and "flipping the altars" is widely seen as a traditionalist move. The Vatican press office quickly downplayed Sarah's comments. Because the issue is a cultural flashpoint between the church's left and right camps, this created a mini-controversy.

But why is this even an issue? And why care about it at all?

While all major Christian denominations, and indeed all major monotheistic faiths, have some form of weekly group worship, for Catholics, Mass is particularly special. This is deeply connected to the strangest Catholic belief, which is the belief in the Eucharist — that the bread and wine used during Mass quite literally become "the body, blood, soul, and divinity" of Jesus Christ. These objects literally become Jesus, who Catholics also believe is God.

Catholics believe that Mass is not simply an occasion to hear important and holy texts, to pray, to reflect, to celebrate as a community — all the things that Protestants, Jews, and Muslims do — but also to encounter God, who literally comes down from Heaven to meet you.

This is why a famous document from the Second Vatican Council called the Mass "the source and summit" of Christian life, and the most important thing the church does. Not prayer. Not right belief. Not good deeds. Those things are important. But in the Catholic view, you will not have those things, or you will get them wrong, if you get the liturgy wrong. At Mass, you are filled with the Holy Spirit, who gives you the power and discernment to be holy in the rest of your life. That is the most important thing.

This is why the Catholic Church says it is a mortal sin — an action that will send you to Hell if you do it knowingly and unrepentantly — to not attend Mass on Sundays. This doctrine has become taboo in the modern Catholic world, but if going to Mass is literally the most important thing you can do as a Christian, and if it really is the place where God is literally coming down from Heaven specifically to meet you, by not going you're essentially giving God the middle finger.

The Mass is that important.

These are ideas that are, in my experience, foreign to most Catholics sitting in the pews — if indeed they sit there at all. If Catholics go to Mass it's because they're happy to, but many of them are there for things that would be, in the Catholic view, nice-to-haves, but not the main part. Community. Celebration. Music. A good homily if you're lucky. Rote habit.

It's not that conservative Catholics dislike folksy, easy-to-sing tunes (as opposed to reverent, classical, or medieval music) on aesthetic grounds (although they often do). It's that privileging this form of music subliminally reinforces the message that going to Mass is a form of entertainment rather than a form of worship.

This is the main virtue of the ad orientem posture. It says, loudly and clearly, "This is not about you." The Mass is supposed to be about God — an act of worship of God. The priest does not have "his back to the people," traditionalists say. He faces in the same direction as the rest of the people: toward God, to worship Him.

Saying "It's not about you!" is a message that is counter-intuitive in a culture that is overly invested in affirmation and self-centeredness. This explains why this conservative Catholic practice turns off so many people. It also explains why it's so needed.

Only a few nerds and wacko birds even seem to care about this stuff. But as a Catholic, I really do believe that the Mass is "the source and summit of the Christian life." It is an act of divine worship and not a community meeting, a literal encounter with God. We ought to treat it that way. And that begins with priests facing God, not us.

It pains me that so many Catholics can't see this. They are visiting the river but not drinking the water that sustains life. What a shame.