Many religions have laws governing ritual purity. The Roman Catholic Church, for example, ruled that under its own laws, a gluten-free wheat wafer cannot be used to confect the Eucharist. Unless you are a canonist or otherwise versed in this sort of thing, please, reader, spare me complaints about this. It is just as parochial to complain about why Jews can't eat bacon, Muslims can't drink wine, and so forth. It is what it is, and there are reasons within the various traditions for these taboos. The point is, gluten-free wheat wafers are unacceptable for the Eucharist in Catholic churches, because the Church teaches that they literally cannot be transformed into the Body of Christ by the priest. For Catholics and Orthodox, the bread literally becomes the flesh of God; you can't just use any old bread, or the ritual will not work. That's why making sure you have the right elements (e.g., wheat that's "kosher" for Eucharist) is so important. That's got The Ochlophobist wondering about whether or not bread made from genetically modified (GMO) wheat can pass these purity laws, both in the Catholic and Orthodox churches. Depending on how the various churches rule on the GMO wheat matter, this could be a huge problem, given how quickly GMO crops are becoming the standard in this country.
Jesus Christ and Gluten
The Catholic Church says that gluten-free wheat wafers cannot be used as the Eucharist.