“Do not consume any blood of birds or animals in all of your dwellings (Vayikra 7:26). …I shall turn My face to the soul that consumes blood and cut if off from amongst its people. For the soul of the flesh is [dependent] on the blood, and I have designated it for you upon the Mizbei’ach to atone for your souls, for the blood shall atone for the soul (17:10-11). Only, be strong and refrain from consuming blood, for the blood is the soul, and do not consume the blood along with the meat.” (Devarim 12:23)

Reason One: Impurity

The Torah describes the blood as the animal’s “soul” in the sense that it is something hidden within the body that provides life (Rav Hirsch). An animal’s blood is coarse and impure like its nature, and if a person would consume it, it would join his own blood and he would adopt some of the animal’s nature. This would ruin his compassionate human nature and elevated intellect that are necessary in order to grasp and fulfill the Torah (Ramban to Vayikra 7:11).

Reason Two: Hashem’s Portion

We may not eat the blood of animals because it is designated to be offered to Hashem, as it is written, and I have designated it for you upon the Mizbei’ach to atone for your souls (Ramban). [Since the blood is considered the animal’s soul, it is offered in place a penitent’s soul. In addition, since the animalistic side of man is responsible for his sins, it is only fitting that he offer an animal’s blood for atonement (see also Rav Menachem HaBavli and Rav Hirsch).]

Reason Three: No Right Over the Animal’s Soul

Hashem initially allowed mankind to eat only grains, vegetables, and fruits. When the animals were spared from the Flood in Noach’s merit, Hashem subjugated them to mankind entirely and allowed their consumption. However, He prohibited us from consuming their blood, since it is considered their “soul,” and a soul has no right to consume another soul (Ramban).

Reason Four: Cruelty

Since the blood keeps the animal alive, and its soul depends on it, its consumption would breed within us insensitivity and cruelty (Sefer HaChinuch §148).

Reason Five: Demonic Practice

At the time of giving of the Torah, there was a common practice amongst demonists to contact demons (sheidim) by drinking blood, in order to hear from them future events. The Torah prohibits all drinking of blood for this reason (Moreh Nevuchim and Seforno; see also Sifri, Re’eh §76).