In the parashah we read last week, Aaron and his sons were dedicated as priests with seven days of inauguration. Now, on the eighth day (shemini means eight) they begin their work as priests, and start by officiating at the ceremonies to dedicate the altar. Aaron, the High Priest, brings forty offerings and a fire comes from God and consumes them. The divine presence is in the sanctuary.
Nadav and Avihu, Aaron's two elder sons next bring an offering, but the text tells us they approach the altar bringing a "strange fire". They have not been asked by God to bring an offering. A fire issues from the altar and consumes them. Aaron is silent during this tragedy. The boy's bodies are removed from the sanctuary and Moses warns Aaron and his two remaining sons, Eleazar and Itamar, not to mourn. God later speaks directly to Aaron, warning him not to drink any intoxicant. The dedication continues. Further rules are given about the sacrifices and then the parashah lists the animals, birds, fish and insects that are permitted or forbidden as food, giving the framework for the laws of Kashrut. Land animals can be eaten only if they have split hooves and also chew the cud. Fish have to have both fins and scales. The parashah also has some of the laws of ritual purity, including that of mikveh, and the Israelite people are reminded to make a difference between that which is ritually pure and that which is ritually impure.
The laws of Kashrut can be sourced back to this sidra - the types of animals, fish, birds and insects that we as Jews may eat, and those we may not. There is no explanation for these laws, just as there is no explanation for what happened to Nadav and Avihu - but both stem from a system that is both rigorous and spiritual. Both are about the spiritual discipline acted out in life. Judaism creates holiness out of the ordinary. Kashrut in relation to food is partly about choosing to partake or abstain, and in so doing to show that we are not ruled by our animal instincts, but always remember that we are human beings who have been created in the image of God.
Kashrut is also a way to make choices in order to encourage spiritual enhancement - for example treif (meaning torn) has at its base meaning a food that has been torn from its source, either through violence or disease. And Nachmanides teaches that the character of the animal we eat will in some way influence us - so we should eat only peaceful and kind animals, and not animals who are predatory or vicious.
The sacredness of food - be it as an offering to be burned or waved before God, or be it the food that we consume - is a primal sense. In the bible, Jews understood about God through food - be it drought or plenty, manna or abundant fruits and grains. Through a consciousness of food, by choosing what, where and when to eat, Jews developed an awareness of the Source of all. Food was the symbol of our relationship with the earth, and that itself is a symbol of our relationship with God. Think back to Genesis when Adam and Eve are thrown out of the garden for eating the wrong fruit - and now they are told that they must earn their own food and work the earth hard for it in order to get what God had given so freely before. Food is the medium through which we learn about our tradition and theology - matza at pesach, cheesecake at Shavuot, the seven species that grow in Israel during Sukkot and so on. Two loaves of bread at each meal on Shabbat - teaching us through food about rest - the manna was given in a double portion in time for Shabbat so that we would not have to go out searching - and working - on that day. Food connects us to the seasons, to the earth and to God. So how we choose to use it, or to abuse it; how we choose to partake or abstain - this can be an important spiritual tool for us to learn, to experience, to teach.