Why did god require a blood sacrifice?
Because blood and human sacrifice were a part of most pre civilized human belief structures. Pre civilized man viewed warm blood as the force that provided life to man. So that magical life force was assumed to provide magical power, and using it in ritual, was the ultimate gift to the Gods. There is little difference between throwing a virgin girl into a volcano to save the village and eating the body and blood of a virgin savior to save your soul. Both rely on human sacrifice, one his half human half God, but still a bloody event.
