The true reason for keeping kosher, is because G-d commanded us to do so. The Torah specifies the details in Vayikra Chapter 11, stating that animals must chew their cud and have split hooves in order to be kosher, fish must possess fins and scales, and a list of forbidden fowl are enumerated.
However, there are also practical benefits for keeping kosher:
Spiritual: The Torah teaches us that non-kosher food affects the Jewish soul. The soul is like an antenna that absorbs waves of spiritual energy. Eating non-kosher food prevents the soul from connecting to spirituality.
Personal Growth: If a person is able to control what he eats and when he eats, he will be able to control other areas of his life too. One who keeps these laws will gain self-control, elevate his soul and overcome animal impulses.
Health Reasons: When it comes to meat, after the slaughtering process, animals are checked for abscesses in their lungs as well as other health problems.
The bulk of the blood - the medium for the development of bacteria in meat - is extracted during the salting process. Shellfish, crabs and other seafood carry many intestinal diseases and are one of the causes of skin disease. Pigs can carry the parasitic disease called Trichinosis; those who abstain from eating pork prevent this danger.
Moral Lessons: We learn not to be cruel - even to animals. "You shall not cook a kid in his mother's milk" - is a verse whose simple and literal meaning forbids us to act cruel. In addition, it is forbidden to slaughter a mother and her young offspring on the same day. It is forbidden to remove the limb of an animal that has not been killed. Slaughtering an animal must be done with the minimum possible pain.
Tradition of Generations: One of the keys of creating a Jewish home is by keeping the Jewish dietary laws. By keeping these laws at home, our connection to Judaism will be rooted in the hearts of our children forever. Since food is usually the center of social events, keeping kosher creates a barrier between Jews and non-Jews, a built-in system preventing assimilation.