Lévitique 17:14

Because the subsistence of the life of all flesh is its blood; it is its life; and I have told the sons of Israel, You shall not eat the blood of any flesh; for the subsistence of the life of all flesh is its blood: whosoever among you eateth it shall be destroyed.

its life depends on its blood The blood is bound up with the breath of life (it is well known that there are two categories of veins coming out of the left side of the heart: those that carry blood, and those that carry the breath), as the olive oil in an oil lamp is bound up with the fire.

therefore I say i.e., therefore I have said , in the current passage. After mentioning wild animals, and birds, which are not sacrificed,

THE BLOOD THEREOF IS ‘B’NAFSHO’ (ALL ONE WITH THE LIFE THEREOF). “Its blood represents its life, since life is dependent upon the blood.” This is Rashi’s language. But it is not correct. Rather, it is possible to explain that the word b’nafsho here means “in its body,” Scripture thus stating, “for as to the life of all flesh, it is the blood in its body.” Similarly [we find the word nefesh meaning “body” in these verses]: ‘Nafsho’ (his person) was laid in iron; seventy ‘nefesh’ (persons); he [the Nazirite] shall not come near to a dead ‘nefesh,’ meaning “a body,” since “the body” of anyone that is possessed of a nefesh (soul) is also called nefesh.
In my opinion Scripture mentioned three expressions with reference to blood, which constitute but one reason. First it stated, For the life of the flesh is in the blood. Then it changed and said [in Verse 14 before us], For as to the life of all flesh, the blood thereof is all one with the life thereof, meaning to say that the blood is the life, and the life is in the blood, as both are mixed together, similarly to wine when diluted with water, in which case the water is in the wine and the wine in the water, and each one is “in” the other. Afterwards it explained [in the second half of Verse 14 before us, stating for the life of all flesh is the blood thereof], that the blood is the very life, meaning to say that both have become one inseparable substance, so that you can never find blood without life nor life without blood, as is known of the air which originates in the heart, that it is the hyly from which proceed all dispositions [of man], supplying the substance which gives nutrition and makes blood, and it is the blood which in turn creates it and sustains it. [The relationship between life and blood is thus] like that of matter and form in all physical creatures, where the one cannot be found without the other. Now our Rabbis interpreted the three punishments of excision which Scripture mentioned with reference to blood in the following way: “One verse prohibits the eating of that blood with which life escapes [when cutting the throat of the offering, since it has been given for atonement upon the altar]; one verse prohibits the eating of blood which escapes when slaughtering [an ordinary, unconsecrated animal], and one verse prohibits the eating of blood, that [of a fowl or wild animal, which when slaughtered] must be covered.” This saying of the Rabbis explains why the punishment of excision was mentioned three times, but the reason for the different Scriptural expressions concerning the life and the blood [of the animal] is as I have explained.

כי נפש כל בשר דמו בנפשו הוא, “for the life-force of all living creatures is its blood” [or contained with its blood. Ed.] (a reference to the way the author described such an almost invisible essence in the blood in his commentary on verse 7).

בנפשו, including this invisible life-force contained therein. This is because the blood contains something almost intangible. Seeing this ingredient is the closest to anything completely intangible in this terrestrial universe, it is an ideal nutrient for the demons and for those who consort with them. The Torah says:

ואומר לבני ישראל, although I have permitted the gentiles the consumption of such lifeblood, I have prohibited it to the Children of Israel already in Leviticus 7,26 seeing that the life essence of living creatures is contained in it while the animal was alive and it is liable to transfer some of these animalistic characteristics kind to the persons ingesting it as food. The Torah wants to protect the Jewish people from absorbing more animalistic tendencies than we already possess.