Some people regard the thought of eating an unclean animal as revolting. Personal taste preferences and appetites are the wrong reasons for avoiding unfit foods. Likewise, health reasons alone are not a good motivation for keeping kosher. A famous rabbi once said that a person should not say, "I think pork is disgusting." Instead he should say, "I would certainly eat it, but My Father in heaven has forbidden me to eat of it, so I will not."
Why does God say that some animals are clean (ritually fit) while others are unclean (ritually unfit)? Surely God, in His wisdom, knew what foods would be good for His people and what foods would be harmful for them. But there is more to it than simply good health. The kosher laws are not God's version of a health food diet.
The laws of what is clean and what is unclean have to do with being able to participate in the Levitical worship system. Things that make a person ritually unfit include death, leprosy, mildew, and human mortality. Some of the animals designated as "unfit" are predators or scavengers that feed on carrion. Some of them carry associations with ritual contamination. Perhaps the Almighty designated some animals as unfit because of their associations with ritual uncleanness. God desires His people to be a kingdom of priests, and that requires implementing ritual concern in daily life.
These are just guesses. We really do not know the reason some animals are called fit and others are not. The rabbis explain that the kosher laws belong to a category of commandment that has no rational explanation. Asking why a buffalo is kosher while a giant sloth is not kosher is like asking why the Sabbath is on the seventh day of the week and not the first day of the week or why the sun rises in the east instead of the west. Some things we have to accept simply because God says so. Who are we to question God? He decided that certain creatures are not food for His people Israel. That is completely within His prerogative.
If we obey God only when it makes good sense to us or when we happen to have a similar inclination, that is not really obedience. This can be compared to a child whose father insisted on an eight o'clock bedtime. On the first night, the child felt drowsy around seven thirty, so he obeyed his father. "How wise my father is to send me to bed at eight," the child thought. The next night, however, he did not feel tired. He could think of no rational reason for going to bed so early. The eight o'clock bedtime mandate seemed arbitrary and unnecessary, so he chose to ignore it. It is not obedience if we only obey when it suits us to do so.
Though we may not be able to deduce why God designated some animals as clean and others as unclean, we do know why He imposed the dietary laws on His people Israel. The Torah tells us that it is a matter of holiness:
You shall not make yourselves unclean with them so that you become unclean. For I am the LORD your God. Consecrate yourselves therefore, and be holy, for I am holy. And you shall not make yourselves unclean with any of the swarming things that swarm on the earth. For I am the LORD who brought you up from the land of Egypt to be your God; thus you shall be holy, for I am holy. (Leviticus 11:43-45)
God gave Israel the dietary laws to make them holy. The word holy does not necessarily refer to a moral or ethical quality. It means to be set apart for the LORD. The distinctive requirements of the Torah's dietary laws accomplish that by forcing the Jewish people to cluster together in communities while limiting their potential interactions with other communities.
Do the prohibtions on eating unclean animals apply to Gentile believers? The dietary laws for God-fearing Gentile believers forbid them from food contaminated by idols, from blood, and from the meat of incorrectly slaughtered animals. Although the dietary laws of Leviticus 11 do not pertain directly to non-Jewish believers, many God-fearing Gentile believers abide by them in keeping with the spirit of the law and in honor of their position as strangers among the Jewish people and servants of the Jewish king.