Leviticus 16:11
Aaron shall bring the bull for his own sin offering to make atonement for himself and his household, and he is to slaughter the bull for his own sin offering. Aaron returns to his personal sin offering bull — the first animal to be slaughtered on the Day of Atonement. The atonement for the high priest himself begins the ceremony. The high priest who will enter the Most Holy Place must be personally atoned for before the blood that covers the community is prepared and presented. The sequence is fixed: personal atonement before communal atonement.