"Rational explanations of this sort (which are seldom the explanations given by the cultures whose rules they seek to account for, anyway) do not even come close to encompassing the full range and specificity of dietary rules, let alone their social power. Nor can they explain why the exact same food (say, pork) is considered imptfe and highly polluting in one culture (say, an orthodox Jewish or Islamic one) and healthy and beneficial in another (say, a traditional Chinese one).
From a comparativist perspective, the truth is that it does not matter what the dietary rules are, as long as there are dietary rules. Put a bit differently, what the dietary codes are about is not the content of the codes themselves, but their functions. And these functions boil down to two: (1) the formation of an individual religious identity and of a set of emotions (purity, pollution, shame, guilt, disgust, and so on) through a necessarily repeated daily act: and (2) the subsequent segregation or separation of a community around these identities, biological acts, and emotions. In short, eating regulations not only help shape and maintain a very particular religious identity; they also form and police a very particular community. They help make a world.
It is not simply food that provides boundaries and meaning, though. Dietary regulations are part of a larger system of rules or purity codes. One might think of purity codes as rules, moods, and assumptions that structure a particular community around a basic binary or set of opposites—in this case, the binary of purity and po|lution—toward the construction and performance of a religious world. By assigning the categories of “purity" and ‘‘pollution'' to daily acts, foods, places, and persons, a society defines not only what a people can eat, but also what it can touch, with whom the individuals belonging to it can mingle or eat, whom they can marry, how ill. wounded, or dead bodies are to be handled. what constitutes a “polluting" sore or disease in that community, what kind of sexual act is proper, and so on. Purity codes are one way in which religious communities structure daily life and maintain both psychological and social boundaries."
--- Comparing Religions / Jeffrey J. Kripal