The Israelites were forbidden from offering sacrifices at any location other than at the tabernacle. Otherwise, it could become easy to follow the practice of worshipping demons, which was strictly forbidden.
Blood is prominent in the worship of God. It was used extensively in the tabernacle worship. Years later, it is the blood of Christ on the cross that saves mankind from his sins. The importance of blood is derived from the fact that, “The life of the flesh is in the blood.”
God’s people were strictly forbidden from eating blood—even from eating meat that had not been properly bled. A person who violated that rule was to be cut off from his people. If, however, a person who had eaten an animal that had not been properly bled, washed himself and his clothes, he would be clean that evening.