Why Keep Kosher
The ultimate answer to your question is "because God said so." Beyond this, however, there are practical, observable benefits to keeping kosher today:
1) Spirituality: The Torah teaches that non-kosher food has a negative effect on a Jewish soul. The soul is like an antenna that picks up waves of spiritual energy. Eating non-kosher food damages the capacity of the soul to "connect spiritually."
2) Self Growth: If you can be disciplined in what and when you eat, it follows that you can be disciplined in other areas of life as well. Kashrus requires that one must wait between milk and meat, and we may not eat certain animals or combinations of foods. All of this instills self-discipline, and enables us to elevate our spiritual side, by making conscious choices over animal urges.
3) Health Reasons: With its extra supervision, Kosher food is perceived as being healthier and cleaner. After slaughter, animals are checked for abscesses in their lungs or other health problems. Blood – a medium for the growth of bacteria – is drained. Shellfish, mollusks, lobsters and crabs have spread typhoid and are a source for urticaria (a neurotic skin affliction). Milk and meat digest at an unequal rate and are difficult for the body. And of course, pigs can carry trichinosis.
4) Moral Lessons: We are taught not to be cruel – even to animals. A mother and her young are forbidden to be slaughtered on the same day, and we "don't boil a kid (goat) in its mother's milk." We must not remove the limb of an animal while it is still alive (a common practice, prior to refrigeration). When we slaughter an animal, it must be done with the least possible pain. And we are reminded not to be vicious, by the prohibition to eat vicious birds of prey.
5) Tradition: One of the keys to making a Jewish home "Jewish" is the observance of keeping kosher. When we keep kosher in the home, our attachment to Judaism and the sacrifices that we make become ingrained on our children's minds forever. And with food so often the focus of social events, keeping Kosher provides a built-in hedge against assimilation. For many, the bridge between past and future is the spiritual aroma of a kosher kitchen.