The sacrifice

It contained the truth—still valid for us to-day—that sin is a reality, which can only be removed by a real event. The atoning sacrifice represents the truth that something must happen, if there is to be peace between God and man, if the communion which has been broken by sin is to be restored. Indeed, there is a further truth behind the shedding of blood in the atoning sacrifices: blood must actually flow, for man has forfeited his life by his rebellion against his Creator and Lord.—Emil Brunner, The Christian Doctrine of Creation and Redemption, 284 (emphasis original)