Chapters 11-15 deal with the regulations on clean and unclean, but we are going to take them chapter by chapter because they each discuss different types of defilement and various states of being clean and unclean. The material that describes that which is clean and that which is unclean can be extremely problematic for modern day life.
Chapter 11 deals with food. Right off the bat we might have a desire to push back against the law all the while asking the question, "How can God prohibit certain foods, especially foods that we eat with some regularity?" Going back to what we have learned from chapters 1-10, God called the people to live lives that reflect their creator, lives that are holy. In order to remain holy, they must be "clean" at all times. What we know, though, is that being clean at all times in nearly impossible. God provides a remedy for this by instituting the Day of Atonement. This special day is the time when sacrifices are made for the express purpose of washing away all the moments in the life of the individual where they were unclean.
Do any of you remember the poster hanging in your elementary school cafeteria that read, "You are what you eat!"? That is a good moniker for chapter 11; you are what you eat. We have certainly seen in modern times that food plays an important role in our health. In modern society, we have the benefit of refrigeration, grocery stores, and a huge variety of produce, dairy, grains, and meat to choose from. At the time when Moses received the law, they were living in the desert with zero refrigeration, zero grocery stores, and only the animals and grains that they managed to carry with them, or the food that God provided. Doctors will now tell you that what we eat effects every system in our bodies and can heal or hurt us. Most of us no longer equate food with holiness, but perhaps we should.
It is important to note that cleanliness and holiness, while intimately linked with one another, are not the same thing. You cannot have one without the other--one must be clean in order to be holy. And it must be stated up front that holiness is an inside job; it is about our attitude and outlook upon life and begins with our thinking which ultimately affects our behavior. Holiness cannot be picked up off the ground and worn like an old coat. Holiness is resident in us and calls us to be aligned with God's purpose for all humanity.
This is all well and good, but there is a huge issue with the Leviticus text that leaves me wanting. While the text is clear about what I should not eat in order to maintain this holiness, it does not give me any kind of rationale as to why certain foods are unclean or why they will defile my body. In modern times, scholars have speculated on all kinds of reasons for the prohibitions in Leviticus. Among the most popular, understanding the hygienic requirements for foods. We now know that certain foods contain tapeworms or bacteria that when consumed can cause all kinds of health issues, including death. We also know that the lack of refrigeration made certain items difficult to cure and eat before they could spoil.
Another aspect of God's relationship with the people of Israel is one of separation. God calls the people of Israel his own. He separates the Israelite people from all others in the region and proscribes specific dietary restrictions, as well as many other behaviors, that are designed to set the people apart from those living around them. From this perspective, we see the God of the Israelites as being unique to the Israelite people.
In the ancient world, every distinct group of people developed their own deity worthy of their worship and devotion. Each group of people called their gods by distinct names and imbued their gods with certain attributes. The people of Israel were no different. The God that they called YHWH or Elohim was unique to the Israelite people. Therefore, in order to maintain this separateness, they had to adhere to laws, especially regarding food, that distinguished them from all other people in the region. Food is often one of the few things that can bring people together. In this case, food was used to create a distinctiveness among this people, set apart from all others.
When Jesus is born into the Jewish world, he begins to reframe the law into a more modern context that is applicable to all people. However, he is still teaching and preaching to his own. It is through the teachings of Jesus and Paul, especially, that we make the leap from God being only for the Israelite people to being a God that is universal in nature.
We may never know God's full reasoning for restricting certain foods from the diets of the Israelite people, but we can at least be aware of the foods that were deemed unclean and unholy, with our continued goal to be holy as God is holy.