Have you ever closed a deal, celebrated your marriage (or its anniversary), or simply spent time with a good friend—without eating something together? When you think of home, is it not in your taste buds that the most elemental memories reside? And what about the food itself—can you get any closer to something than by ingesting it into yourself and turning it into your own flesh, bone and blood?

Tell me what, how, where and with whom you eat, and I’ll tell you who and what you are.

Numerous explanations have been offered for the Torah’s kosher dietary laws. Some point out the health benefits. Others dwell on the unifying effect these laws have on a dispersed people, and their role as a shield against assimilation. Nachmanides, the great 13th-century sage and Kabbalist, explains that “the birds and many of the mammals forbidden by the Torah are predators, while the permitted animals are not; we are commanded not to eat those animals possessive of a cruel nature, so that we should not absorb these qualities into ourselves.”

But perhaps the most basic reason (insofar as a divine command can possess a “reason”) is that presented by the Torah itself in the closing verses of its chapter on the dietary laws:

To differentiate between the impure and the pure, between the animal that may be eaten and the animal that may not be eaten. (Leviticus 11:47)

“To differentiate,” lehavdil in the original Hebrew—this single word defines man’s uniqueness as a moral creature. Or, in the Torah’s terminology, a “holy” person.

As our sages point out in their commentary on this verse, the concept of lehavdil applies only to two ostensibly similar things. Cows, too, differentiate, between a nutritious grass and a poisonous weed. But the kosher-observant shopper will differentiate between a piece of meat from an animal that was slaughtered by a certified shochet in accordance with the detailed laws of shechitah, and a piece of meat from an animal that was simply killed in an abattoir. No laboratory will discover any physical difference between the two. But the Jew accepts the first and rejects the second. And if he unwittingly brings the second into his kitchen, he will blowtorch the pan that cooked it and discard the china on which it was served.

Morality is the capacity to accept that there are things to be embraced and things to be rebuffed. Sometimes the desirability or undesirability of a thing is obvious; sometimes we can smell the difference, and sometimes we can understand it. But if that’s where it stops, we’re nothing more than cows avoiding the poison.

The point at which we begin to lead moral and holy lives is the point at which we say: “There is ‘Yes’ and there is ‘No’ in G‑d’s world. These are objective truths, established by the Creator of reality. Often I will find that the ‘Yes’ things give me pleasure, safeguard my health, preserve society, and fulfill me spiritually, while the ‘No’ things achieve the opposite. But this is not what makes them ‘Yes’ or ‘No.’ On the contrary: because a thing is morally positive, it will invariably occupy a positive place in my life; because a thing is morally negative, it will inevitably hurt me. But my need to affirm the ‘Yes’ and reject the ‘No’ stands above these considerations, which are the result, not the source, of the intrinsic difference.”

Of course, every time the Torah tells us to do something or not to do something, it is making this point. But nowhere is the imperative lehavdil as fundamental as when it dictates what we should eat and what we should not. Nowhere is it as intimately woven into our lives as when applied to the act of eating, by which the eater and the eaten literally become one flesh.

If you accept a yes/no line of demarcation across the diameter of your dinner plate, then—and only then—have you mastered the art of holiness.