Deuteronomy 12:23
Only be sure that thou eat not the blood: for the blood is the life; and thou mayest not eat the life with the flesh. Only be sure that thou eat not the blood: for the blood is the life; and thou mayest not eat the life with the flesh.
The blood is life and must not be eaten with the flesh. For that reason the blood of slaughtered animals was to be drained out rather than consumed with the meat. This draining of the blood was required to preserve health. Blood was also to be regarded as sacred because it represents life and stands as an emblem of the Son of God.