I Never Drink…Blood.By Rabbi Jack Abramowitz
As we said, if anyone offers a sacrifice outside of the Temple (or Tabernacle), the penalty is kareis (spiritual excision). If anyone eats blood, the penalty is also kareis. This is a serious sin because the life force of an animal is in the blood and G-d has directed that blood be used on the altar to effect atonement, not as food.
When a person catches a bird or an animal (chaya – like a deer, as opposed to domesticated livestock like cattle), and slaughters it for food, he must cover the blood with dirt.
If an animal dies on its own (as opposed to being ritually slaughtered), or has a medical defect that will ultimately result in its death, it may not be eaten. If someone does eat such a thing, he must immerse himself and his clothes in a mikvah and he will be unclean until nightfall.
Next, G-d told the Jews that they had to adhere to Jewish standards of behavior, not emulating the ways of others among whom they may live.