There is not a lot of widespread agreement on the rationale behind Kashrut, and there is even disagreement on whether or not we, as mere mortals, should even be seeking to understand G-d's law. Operating on the assumption that it always preferable to seek to understand, rather than to blindly obey, I find some arguments for the purpose of Kashrut way more compelling than others. In fact, the two that make most sense to me are, while not mutually exclusive, at least incompatible. On the one hand, Mary Douglas, in her book, Purity and Danger (London: Routledge & Kegan Paul Ltd, 1966) suggests that the Kashrut laws are a set of prescriptions and proscriptions designed to establish a pattern of wholeness (and therefore holiness) reflective of G-d's own holiness and perfection. Every act of eating, and even menu planning becomes a meditation on holiness. Animals that are kosher to eat are animals that conform perfectly to descriptions of wholeness. Land mammals that are good to eat have cloven hooves and ruminate, tasties from the water have fins and scales, birds have feathers and are capable of flight, and edible insects have to locomote by hopping, not swarming. Potentially delicious meals that either do not conform to these categories of cleanliness, or inhabit a grey area, fall short of perfection, and are therefore not Kosher.
On the other hand, it also makes sense to me that the Kashrut laws might be a way of maintaining a distinct society, rather than a holy one. Creating a very specific set of rules governing what may, or may not be eaten is an effective way of minimizing contact between different groups. For example, pigs don't offer much in the way of wool, milk or hide, and they consume grain: they probably weren't kept as livestock by the Israelites. The injunction against eating the flesh of pigs (and other strange animals) is maybe a way of keeping the Israelites separate by preventing them from sitting down to eat with other groups and cultures. Familiar and homegrown = kosher and delicious, strange and unfamiliar = contrary to G-d's will.
And while I think that these arguments are coherent and intelligible, they don't do much for me in terms of guiding my behaviour. I think all of G-d's creatures are delicious (with the possible exception of the strange and unfamiliar hopping insects, to say nothing of the swarming ones), and they all taste even better with butter on top.
I hope this doesn't offend you.