The genius of the eucharist, in strictly human terms, is in its simplicity: bread and wine, the everyday foods of Mediterranean antiquity, enter the ritual process to become body and blood. The elements are plain and common, so humble as to be almost embarrassing. Yet they represent the nearly miraculous transformation of nature’s abundance by human ingenuity and labor. Body and blood, the ritual products, are scarcely less so. Bread becomes body all the time, in a sense, wherever it is eaten, imparting its peculiar alimentary virtues to a small but complex animal that then, for example, sits and types words onto a screen.

Whether as a holy sacrament or a randomly-generated meme, the practice is perfect. Bread, body, nature, culture, always at hand and always primed for a miraculous transformation of the humble.

So it should come as no surprise that Christian churches sometimes go to considerable lengths to protect and preserve the practice of the eucharist from variations or influences that could distort or obscure its compelling core. When the Vatican issued expanded guidelines for the elements to be used in Catholic celebrations of the eucharist, it included a restatement of a prohibition of totally wheat-gluten-free hosts. This was often reported as something of a snub of the Celiac sufferers (or gluten intolerant) among the faithful.

But reading through the directive and the supporting documentation, I was struck by their attempts to accommodate communicants who can’t tolerate some essential aspect of the rite. The bread for the host can be so low in gluten as to qualify for “gluten-free” labeling, apparently. The wine can be a barely fermented drink called “mustum” (a word I have never encountered outside of Catholic liturgical documents). Anyone who cannot receive the bread or the wine can commune fully in one or the other. And in a rather touching detail, a priest who is too infirm to stand at the altar, as canon law requires, can get a dispensation to preside while seated.

This blend of punctiliousness and latitude is characteristic of the Catholic Church, but hardly unique to it. It’s a feature of many religious traditions that have worked through centuries to define a stable core of practice within the shifting exigencies of daily life. If a Muslim can’t find water for ablutions before prayer, she can use sand. A shabbos goy can give an observant Jew a ride in his car.

In a world as purely pragmatic and as sensitive to the need for exceptions as ours, these partial accommodations can seem not so much ingenious as nit-picky, or, on the other hand, hypocritical. A casual reader of religion stories, without access to the endless history of arguments, justifications, and adjustments in which the document or development in question is merely the latest, could be forgiven for reading them cynically. Regulations can seem opposed to the human need they ought to be addressing. The boundary that defines a practice can easily be interpreted as a mere exclusion and not an attempt, however unnervingly precise, to preserve something good and essential within it.

But if our preconceptions as readers (and writers) of religion stories have changed with the times, the dilemmas themselves haven’t. Perhaps the enduring appeal of Vatican policy write-ups in news outlets is not in the unique concerns of Catholicism but in Rome’s unique power to specify issues in religion more generally. Discerning the center of a practice in the midst of the prosaic task of defining its boundaries (20 parts per million or less!) is, if nothing else, really interesting. It raises compelling questions. Why, after all, can’t Jesus just ditch the gluten entirely and become present in a different grain?

The answer, as far as the official documents are concerned, is that only bread made of wheat is “valid matter” for the sacrament. Bread made without any wheat is not really bread, and so can’t fulfill Christ’s command to “do this in remembrance of me.” The definition of “bread” does the necessary work.

This is not an answer everyone finds satisfying. If, like me, you are not persuaded by the definition of female humans as invalid matter for the sacrament of ordination, you probably won’t find the definition of non-wheat bread as invalid matter for the eucharist either. But satisfying or not, definitions are inevitable. Whether the wrong elements are resistant to being transformed into Christ, or they simply impede our own ability to discern and practice the sacrament properly, surely some things suit and others don’t. An early moment of scandal in my Christian life occurred when someone blithely described using chips and Pepsi for the eucharist. I still can’t give a completely coherent account of why that’s wrong, but it still seems pretty wrong to me.

And it is an especially poignant question when we abstract from the hot-button topic of gluten to the more nebulous challenge of translating a practice across cultures. Where wheat (or wine) is unknown, choices have to be made. The Catholic Church has stuck to its guns, insisting that the elements be imported where they are unknown. In this way, the specific food culture of Jesus’s time is a link across ages and cultures. Bread, whether common or exotic, becomes a sign of universality. Protestant churches, on the other hand, have sometimes embraced local variations of “staple food and festive drink” for the sacrament. With local foods, the sacrament reflects universality by analogy to the world of Jesus, in the ordinariness of a community’s own daily life. Everybody’s gotta eat.

This is a serious dilemma for a religion based on the claim that the God of Israel became incarnate in a Jewish man in first century Palestine. It’s the reason Bible translations in breadless regions can struggle to render Jesus’s words in John 6:35—”I am the bread of life”—in an intelligible idiom. “I am the sweet potato of life.” “I am the rice of life.” Can Jesus be “bread”—and can bread be Jesus—where bread is unknown, or consumed only by a rarified (or colonial) elite? The ritual is predestined to change, either in its form, or in the way people experience it. Somewhere a leap must be made, if not in the words and the matter themselves, then in the imagining and the eating habits of the people who must translate the exotic, or even toxic, food into something common.

The gluten guidelines show at least some consideration for the fact that not everyone’s leap into the meaning of the eucharist is the same. Whether by engineering or importation or accommodation, an act with universal claims must somehow be made available to anyone. A ritual can bend pretty far, and in more than one direction, without breaking. What needs it bends for, and how far it can bend to meet them, may or may not be adequately answered by rules for the host. The only certainty is that new needs will arise, new questions will be asked, and the central practice of Christianity will find new ways to adapt.