R' Shamshon Rafael Hirsch's approach to the dietary laws is excerpted in this article by Rabbi Avi Weiss
Is it possible that food could similarly impact on one's spiritual
well-being? This in fact is the position of Rabbi Samson Raphael
Hirsch in his explanation of kashrut (the dietary laws).
The characteristics of kosher animals point to their being more
passive in nature. In Hirsch's words: "If we look at the signs for
clean animals they appear plant-like. As they chew the cud, the food
consumed passes through two stomachs, is driven up the gullet again
and chewed for the second time. Thus, these animals spend a great deal
of time in the absorption of food. The cloven hooves of the permitted
animals also seem to have been created more for the mere purpose of
standing than for being used as weapons or tools."
The same is true concerning fish. To be kosher, fish must have fins
and scales. (Leviticus 11:9) Not coincidentally, fish that have these
characteristics are by and large more peaceful in nature. The more
aggressive fish fall into the category of the prohibited. Moreover,
birds of prey are by and large enjoined. The rule holds fast. The more
aggressive animals and fowl are prohibited. The more passive are
permitted.
Of course, not everyone who consumes kosher food leads lives of inner
peace. There are troubled people who eat kosher, just as there are
fine people who do not eat kosher. Nonetheless, the ritual of kashrut
may help us become more conscious of our responsibilities to live
ethical lives.
The balance between outer action and inner feelings is especially
discernible in the laws of forbidden and permitted animals. Note, that
chewing the cud is an internal characteristic as it deals with the
inner digestive system. In contrast, cloven hooves are an external
characteristic. One merely has to look at an animal's foot to detect
whether this criteria has been met. Perhaps, just perhaps this teaches
that to be kosher one's behavior must not only be correct, but
inwardly pure.
Whether these rationales are satisfactory or not, the prohibited foods
teach us discipline. They remind us that in the end, God is the
arbiter of right and wrong. Notwithstanding, the kashrut laws carry
powerful ethical lessons--lessons that can help ennoble and sanctify
our lives.