In Parshat Shemini the Bechor Shor provides his own explanations as to why some animals and foods are kosher, and other are not.
Any animal that has true hoofs, with clefts through the hoofs, and that chews the cud—such you may eat. The following, however, of those that either chew the cud or have true hoofs, you shall not eat: the camel—although it chews the cud, it has no true hoofs: it is impure (tameh) for you. (Vayikra 11:3-4)
In these verses, the Torah provides criteria for identifying kosher and non-kosher species. With regards to the non-kosher animals the Torah notes both that they can not be eaten and that they are tameh, impure. The Bechor Shor sees the additional identification of these animals as tameh, impure, as providing a reason for the prohibition. He writes that whenever the Torah uses the word tameh, it means mezuham ve’maus, filthy and disgusting. The non-kosher species of animals are filthy and disgusting and that is why they may not be consumed.
When you see a pig wallowing in the mud, it certainly looks filthy and disgusting. The challenge of course is that there are plenty of non-kosher animals, like a lion or tiger, that can seem quite majestic and ostensibly not filthy and disgusting. It is not clear how the Bechor Shor would answer this question.
This approach of the Bechor Shor, despite its challenges, does help to explain the juxtaposition of the kosher laws to the laws of the Temple related at the beginning of the parsha. A person who works in the Temple or comes to the Temple to bring a sacrifice should be holy and pure. The Temple was a beautiful, awe inspiring place and therefore anything which contaminates a person and causes him or her to become filthy and disgusting would detract from the purity of the Temple. Thus, one who has come in contact with such dirty animals is not allowed access to the clean Temple.
The Bechor Shor also presents an explanation for why blood and certain fats of the animal are prohibited for consumption. These items are not described as tameh, impure, by the Torah and therefore have a different rationale for being prohibited. The Bechor Shor writes that the blood and fats of the animal were critical in the sacrificial order and were therefore designated as holy. They are, he writes, the portion of the king, and therefore not fit for our consumption.
This approach of the Bechor Shor seems to be an explicit verse:
For the life of the flesh is in the blood, and I have assigned it to you for making expiation for your lives upon the altar; it is the blood, as life, that effects expiation.(Vakira 17:11)
Commenting on this verse the Bechor Shor writes that blood is prohibited for two reasons. It is the soul of an animal and therefore not fitting to eat, and it has been designated to be offered on the altar and therefore should not be used for anything else.
Finally, the Bechor Shor presents a reason for the prohibition of Orlah.
When you enter the land and plant any tree for food, you shall regard its fruit as forbidden. Three years it shall be forbidden for you, not to be eaten. (Vayikra 19:23)
The Bechor Shor writes that the first fruits of a tree should be offered to God because it is not proper to benefit from something without first proving thanksgiving. However, the fruits that a tree produces during its first three years are not high quality fruits and therefore it would not be fitting to offer such fruits to God. Only by the fourth year are the fruits robust enough to be offered, and therefore the fruits of the first three years can not be eaten by anyone – they can’t be offered to God because they are not nice enough and they can’t be eaten by the owner because thanksgiving has not yet been offered.