Leviticus 17:11

Because the subsistence of the life of all flesh is in the blood, and I have given it to you for a decree, that you shall bring the blood of the victim unto the altar to make atonement for the blood of your lives, because the blood of the victim is to atone for the guilt of the soul.

atones with the soul The blood secures atonement by means of the animal spirit which it formerly contained (in the sense of “a soul for a soul” [Exodus 21:23]). Other people interpret atones with the soul as a reference to the human soul, as in, to atone for your lives [literally: for your souls]. This interpretation is senseless, because it would make the verse redundant.

FOR THE LIFE OF THE FLESH IS IN THE BLOOD; AND I HAVE GIVEN IT TO YOU UPON THE ALTAR TO MAKE ATONEMENT FOR YOUR SOULS. The sense of this verse is to state that He forbade us [to eat] blood because He has given it to us to be upon the altar and to effect atonement for our souls, and it is therefore the part dedicated to G-d, just as is the case with the forbidden fat. And if one should ask: “Why then has He forbidden us to eat the blood of a wild animal and that of a fowl, from which offerings are not brought?” We will dismiss the questioner by saying that it was His wish to keep us far away from eating any kind of blood, in order that we should never make a mistake therein [and eat forbidden blood as a result of failing to distinguish between one kind of blood and another]. In the case of fat, however, He did not [categorically] forbid all kinds of fat, because [the permissible kind of fat] is distinguishable from the non-permissible.
Now the Rabbi [Moshe ben Maimon] wrote in the Moreh Nebuchim that the Chaldeans loathed blood, considering it impure, and only those who sought to establish contact with the demons and to foretell the future would eat it. Now the Torah always seeks to destroy these foolish theories, by [ordaining measures which are] contrary to their ideas. Therefore He prohibited the eating of blood and chose it as the means of purifying [the impure] by means of the sprinklings thereof, and to throw it upon the altar of G-d for atonement. Therefore He said, I will set My face against that soul that eateth blood, just as He said with reference to him who gives of his children to Molech,. because this [practice of eating blood] leads to a kind of idol worship, such words not being stated concerning any other commandment. Now these words [of Rabbi Moshe ben Maimon] are sensible in themselves, however the verses do not indicate [that the reason for the prohibition against eating blood is] so [as the Rabbi has said], for they always state the reason for that prohibition to be, For as to the life of all flesh, the blood thereof is all one with the life thereof; For the life of the flesh is in the blood. And in the Book of Deuteronomy He again states, Only be steadfast in not eating the blood; for the blood is the life; and thou shalt not eat the life with the flesh.
It is proper, therefore, to explain the reason for the prohibition against eating blood by saying that G-d created all lower creatures for the …