Why is the shedding of blood necessary for forgiveness?

Les teaches that from the very onset of the human experience God has demanded a blood sacrifice before there can be a remission of sin. He explains this goes back to God's sovereign mind in creation: God placed the life of living things in the blood. Science did not catch on until about World War II that life is in the blood. It is His prescription, not anyone else's, that without the shedding of blood there can be no forgiveness, and we cannot bypass it. Les notes that many people today do not want to hear anything about the blood—it has almost become taboo—but you cannot escape it in Scripture; you cannot go around it, over it, or under it, but must face it head on. He also points to the Jews under the safety of the blood: they did not deserve it, but the blood guaranteed their safety, and it was the blood applied to the door that guaranteed the angel would pass over. Though they exercised faith, it was the blood that secured them. He then moves back to the New Testament and Romans, stressing that it is the Apostle Paul who has the revelations that pertain to us, where things not covered in previous Scriptures come out in full flower.