Hebrews 9: 7;17 - But only the high priest ever entered the Most Holy Place, and only once a year. And he always offered blood for his own sins and for the sins the people had committed in ignorance. That is why even the first covenant was put into effect with the blood of an animal.
Hebrews 12:24 - You have come to Jesus, the one who mediates the new covenant between God and people, and to the sprinkled blood, which speaks of forgiveness instead of crying out for vengeance like the blood of Abel.
Sin brings shame and it is recorded that the Blood of the animal was used in Genesis 3:21. It is often taught that after the first sin was committed, God wanted to show Adam and Eve that sin has consequences, and so He slew an animal in front of them and made clothes for them from the dead animal. God killed (made the first sacrifice by killing) an animal for the remission of Adam and Eve’s sins.