Leviticus 17:13
And whatsoever man there be of the children of Israel, or of the strangers that sojourn among you, which hunteth and catcheth any beast or fowl that may be eaten; he shall even pour out the blood thereof, and cover it with dust. And whatsoever man there be of the children of Israel, or of the strangers that sojourn among you, which hunteth and catcheth any beast or fowl that may be eaten; he shall even pour out the blood thereof, and cover it with dust.
Any man of the children of Israel or of the strangers sojourning among them who hunts and catches any beast or fowl that may be eaten is commanded to pour out its blood and cover it with dust. Permitted meat may be eaten only after its blood has been carefully drained, and meat from a creature whose blood has not been drained is forbidden. The ban is perpetual in all dwellings and covers not only beasts for sacrifice but all cattle used for food and hunted game. Blood was not to be eaten because it was regarded as the life.
Blood is sacred because its shedding came through sin and it symbolizes the blood of the Son of God, whose shedding alone makes atonement and cleansing from sin as shown when blood cleanses the sanctuary from the sins of the people, so if there had been no sin there would have been no shedding of blood. The law keeps clear and definite ideas between the sacred and the common, in contrast to idolatrous sacrifices where people eagerly drank the flowing blood and gained confused ideas. Gentiles commonly drank sacrificial blood or used blood in food. The instruction to drain blood was given to preserve health and strength.
Fat belongs with the sacrificial offerings and is never suitable for food, and eating it brings disease as the sure result. Using blood as food was considered sinful. The rule shaped Jewish food customs and their practice of draining slaughtered animals, and made eating together difficult and a cause of offense when Gentile converts consumed blood. Israel violated the law against eating flesh with its blood when, faint from hunger after fighting all day under Saul's vow and curse against eating until evening, they fell upon the spoil as soon as the restriction ended and devoured flesh without properly draining the blood still in it.
The verse belongs to the ritual law forbidding Israelites and resident foreigners to taste or eat blood, which explains why the Jews took Jesus' words about eating His flesh and drinking His blood as a literal, offensive and sacrilegious command.