Since the beginning of time God required animal sacrifice from the High Priest to atone for the peoples sin. My guess is that animals are sinless so their blood was a representation of the future Christ' blood. Jesus didn't have to die, He chose to die. He became the One Perfect sacrifice, His blood was like no other. Not of human origin so there was no original sin from Adam in His blood. We don't need to offer Rams, Bulls and Goats anymore.
Jesus' blood washes all of our sin as if we had never sinned. When we stand before God at the judgment, all God will see is Jesus and His perfect plan of redemption for those of us who believe in Him. If God had created us as robots, to worship and obey Him, no sacrifice would need to be made. Because God gave us Free Will to choose to Love Him and Worship Him, sin would be part of every persons life so we would all perish in our sin.
God is holy, fair and just...Sin must be punished...Thank God Jesus took the pain of all of our sin upon Himself so that we could be brought into the presence of God Almighty.