None of this is actually in the Bible (JFTR).
Polycarp pretty much nailed the explanation, Christian sacrificial soteriology has its roots in ancient animal sacrifice. People used to sacrifice animals because they thought that was what God wanted. They assumed that God was especially partial to perfect, unblemished “holy” animals. The Pascal lamb was a pure white lamb with no flaw. After the crucifixion, early Christians needed to find a way to explain the execution of their leader in spiritual terms. He became identified as a surrogate for the Pascal lamb, the ultimate animal sacrifice, God in human form sacrificing himself for all mankind. Why God would require a blood sacrifice is simply an archaism. Why do any gods require any sacrifices? Frankly, in very ancient times, people thought they were feeding the gods. It was just that simple. Later the animal sacrifices were seen as more symbolic – people were giving the best they had to God to show proper respect – and the Pascal-surrogate symbology has been heavily mystified with Jesus, but the actual mechanism for sacrifice bringing atonement still boils down to an arbitrary demand by God.
Frankly, without Adam and Eve/Original sin, the whole thing falls apart anyway.