In the Scriptures, "blood" always symbolises Death. It does not symbolise Life.
The presence of blood, such as on the door posts or before the altar, indicated that the lamb had been slain.
The Jews were told to ensure the beast was dead before they could eat it, indicating this by draining the blood from the meat. They were thus rejecting heathen practice of ripping flesh from a living animal and eating the quivering flesh in the belief that the blood would pass on the animal's qualities.
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