11 For the life of a creature is in the blood, and I have given it to you to make atonement for yourselves on the altar; it is the blood that makes atonement for one’s life.
This idea of the life being in the blood is repeated three times the next four verses. It must be an important idea. It is important because it teaches that sin costs a life. When there is sin, someone must die in order to restore the relationship with God. Only life restores death. That is why Jesus needed to die so that we might live. He gave up His life so that we could be born again. It is not the physical blood that brings life to the one sacrificing, but the pouring out of the life. One life given up, one life restored. One animal sacrificed so that sin might be forgiven and relationship restored with God. Notice that only one animal gets sacrificed to the sins of all the people. Jesus gave up His life so that everyone could be restored to fellowship with God.
The Arnold Journey 