Ulla Bira'ah opened a discourse in the name of Rabbi Simeon bar Yohai. He said: This may be compared to the case of a man who went to a threshing-floor, taking his dog and donkey with him. He loaded five se'ah on his donkey, and two se'ah on his dog. The donkey walked along, but the dog panted, so the man took one se'ah and put it on the donkey. The dog, nevertheless, kept on panting. The man said to his dog: 'When you are laden you pant, when you are not laden you also pant.' Thus it was with the non-Israelite nations; they were unable to endure even the seven precepts accepted by the descendents of Noah, so God took these off them and put them on Israel.
Why keep kosher?
The rabbis are looking for an answer to the inexplicable question, asked by my own five-year-old daughter not so long ago about Shabbat (and I'm sure once she learns about the existence of pepperoni pizza, kashrut will be next): "Why can't Jewish people watch TV on Saturday when other people can?"
The search for ta'amei ha-mitzvot, reasons for the Commandments, goes back nearly as far as the Commandments themselves. The passage above from Leviticus Rabbah is one example. As the Torah passage launches into the details of the laws of kashrut, the rabbis run up a series of midrashic musings on why Jews alone are given this strange set of laws.
At its root, the question is about the particularity of halakhah. Not "Why this animal but not that animal?" so much as "Why us and not them?" with a valence of pride, pasted on by way of a rabbinic lens that is hopeful of encouraging adherence to this seemingly haphazard diet. The rabbis here paint halakhah as something special; something given to the reliable, hardworking, useful donkey by a master in need of work to be done. But they are also realistic: it is harder to be a donkey than a dog. It is harder to be a mitzvot-adhering Jew than it is to be . . . well, a non-mitzvot-adhering Jew.
The midrash here is both disquieting and inspiring (not unlike the laws of kashrut at their core). It is disquieting because of the comparison of the non-Jewish nations to a dog, while Israel is held up as that useful, hardworking, reliable donkey. But it is inspiring, too, because, in this vision, halakhah is the Jewish way of doing God's work. The details of kashrut as listed in Parashat Sh'mini might beg the question "Why?" but the rabbinic answer of Leviticus Rabbah 13:2 is because God gave us a job to do. Keeping kosher is one way of expressing allegiance to a master in grave need of helpers to perfect an imperfect world—one way of letting God and one another know that the people chosen to serve in this particular way are still at work.