This great verse contains a wealth of scientific and spiritual truth. It was not realized until the discovery of the circulation of the blood by the creationist scientist William Harvey, in about 1620, that biological "life" really is maintained by the blood, which both brings nourishment to all parts of the body and also carries away its wastes.
Its spiritual truth is even more significant. The blood, when shed on the altar, would serve as an "atonement" (literally, "covering") for the soul of the guilty sinner making the offering. In fact, the "life" of the flesh is actually its "soul," for "life" and "soul" both translate the same Hebrew word (nephesh) in this text. When the blood was offered, it was thus an offering of life itself in substitution for the life of the sinner who deserved to die.
Human sacrifices, of course, were prohibited. No man could die for another man, for his blood would inevitably be contaminated by his own sin. Therefore, the blood of a "clean animal" was required. Animals do not possess the "image of God" (Genesis 1:27), including the ability to reason about right and wrong, and therefore cannot sin. Even such clean blood could only serve as a temporary covering, and it could not really "take away" sin. For a permanent solution to the sin problem, nothing less was required than that of the sinless "Lamb of God, which taketh away the sin of the world" (John 1:29). "Neither by the blood of goats and calves, but by His own blood He entered in once into the holy place, having obtained eternal redemption for us" (Hebrews 9:12). Since His life was in His blood, He has "made peace through the blood of His cross" (Colossians 1:20). HMM