 The book of Leviticus describes the complex system that God had set up that involved animal sacrifices and a sacrifice to atone for the sins of the people. And the priest would take the animal and kill it and sprinkle the blood on the altar and burn the carcass on the altar. God's law was very specific. They couldn't bring a sickly or a crippled animal to do this. It had to be without spot and without blemish.