Why is gluten required?
Without getting in too deep into the workings of the Catholic faith - in a nutshell, wheat bread and wine made from grapes are at the heart of the sacrament of Holy Communion. This is based on the belief that Christ compared his body to a grain of wheat and his blood to grape wine prior to eating bread and drinking wine at the last supper.
The Catholic Church uses bread to symbolize the body of Christ. In its simple form, bread is made with wheat flour and wheat flour contains gluten. This is why the Catholic Church uses communion hosts or bread that contain gluten and, like the last supper, invites everyone in mass to partake.