Leviticus 11:46
This is the law of the beasts, and of the fowl, and of every living creature that moveth in the waters, and of every creature that creepeth upon the earth: This is the law of the beasts, and of the fowl, and of every living creature that moveth in the waters, and of every creature that creepeth upon the earth:
This is the law given through Moses to Israel and the Hebrews distinguishing animals unfit for food from those that could be eaten, covering beasts, birds, creatures in the waters, and creatures creeping or moving upon the earth, and specifying which animals were least objectionable for food. It belongs to instruction that included health principles and sanitary laws and formed part of the strict training Israel received in the wilderness before entering Canaan. It forbids eating any unclean thing, and forbids eating and touching swine's flesh as unclean along with other unclean animals, birds, and fish. Those forbidden animals were not the best articles of food and were never designed to be eaten under any circumstances.
Permitted meat was further restricted by forbidding its fat and blood and by excluding creatures that were torn, had died naturally, or had not been properly drained of blood. The restrictions were wise prohibitions for health given to preserve life and health by keeping the blood pure through simple, healthful food, not an arbitrary exercise of authority. Swine's flesh and certain other animals were prohibited because they fill the blood and system with impurities and humors, pollute the blood, and shorten life. Swine's flesh was especially hurtful in that warm climate, often producing leprosy, with influence far more injurious there than in a colder climate. Swine were useful as scavengers permitted to run free to devour decaying substances that would poison the atmosphere, which preserved health.
If Israel had submitted to these prohibitions God would have removed everything injurious to health and suffered no sickness to be among them, and the verse remains the basis for choosing clean, wholesome food. Letting appetite control reason benumbs the fine sensibilities so sacred things are placed on a level with common things. The food appointed to Daniel and his companions at the king's table included those unclean meats with wine, and refusing them obeyed the will of God as the supreme law of life, kept mind and physical structure in the best condition of health to do God's service, and kept the intellect clear and undimmed to stand as representatives of true religion. That refusal prevented enfeebling of brain and muscle, and protected physical, mental, and moral powers from being imperiled by indulgence of appetite.
The rules did not require straining all water or drinking water lest it contain the smallest insect classed with the unclean animals. That was an unwarranted extreme added by the Pharisees and religious leaders, who perverted the law, multiplied restrictions and ceremonies, and turned its rules about uncleanness into trivial burdens that burdened people and distracted them from true religion.