Ramban (Leviticus 17:11) composed a lengthy comment on the prohibition to eat blood, and we cite it in its totality. This topic presents a good illustration of a theme that regularly appears in Ramban’s Commentary on the Torah: he will present a rationalistic view (in the case at hand, that of the Rambam) concerning a topic, but because of, among other reasons, his commitment to peshat, the plain sense of the words of the Bible, he rejects this interpretation in favor of another one. Ramban writes as follows:

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 (God) 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 God, just as is the case with the forbidden fat. And if one should ask: “Why then has He (God) forbidden us to eat (even) 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 (God) did not (categorically) forbid all kinds of fat, because (the permissible kind of fat) is distinguishable from the non-permissible.

 Now the Rabbi (Moses ben Maimon) wrote in his Moreh Nebuchim (III: 46) 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 (God) prohibited the eating of blood and chose it as the means of purifying (the impure) by means of the sprinklings thereof (such as in the case of the leper, Leviticus 14:14), and to throw it upon the altar of God for atonement. Therefore He said, I will set My face against that soul that eats blood (Lev. 17:10), just as He said with reference to him who gives of his children to Molech (Lev. 20:6- And I will set My face against that soul), because this (practice of eating blood) leads to a kind of idol worship, such words (that is, the harsh language of the Bible) not being stated concerning any other commandment.

Now these words (of Rabbi Moses 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 Rambam has said), for (the biblical verses) 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 (Lev. 17:14); For the life of the flesh is in the blood (Lev. 17:11). And in the Book of Deuteronomy He (God) again states, Only be steadfast in not eating the blood; for the blood is the life; and you shall not eat the life with the flesh (Deut. 12:23).

It is proper, therefore to explain the reason for the prohibition against eating blood by saying that God created all lower creatures for the purpose of man, since only he amongst them recognizes his Creator. Nonetheless, He did not at first permit man to eat anything except for vegetation, but no living creatures at all, just as it is stated in the Chapter of creation where it is said, Behold, I have given you every herb yielding seed etc. for food (Genesis 1:29). But when the flood came and they (the lower creatures) were saved  by the merit of Noah, and he brought offerings from them to God which were more acceptable before Him, (Genesis 8:21), He gave man permission to slaughter (and eat animals), since their existence was because of man. Thus He permitted man to use their bodies for his benefits and needs because their life was on account of man’s sake, and that their soul (i.e., blood) should be used for man’s atonement when offering them up before Him, blessed be He, but not to eat it, since one creature possessed of a soul is not to eat another creature with a soul, for all souls belong to God. The life of man just as the life of an animal are all His, even one thing befalls them, as one dies, so dies the other yes, they have all one breath (Ecclesiastes 3:19).

Now in the opinion of the Greek philosopher (i.e., Aristotle) as interpreted by those who scrutinize his words, it was out of the Active Intellect that there emitted a very fine and bright flash and glitter of light, from which came forth the spark which is the soul of the animal. It is thus in a certain sense a real soul. It (i.e., the animal) therefore has sufficient understanding to avoid harm, and to seek its welfare, a sense of recognition towards those with whom it is familiar, and love towards them, just as dogs love their masters, and they have a wonderful sense of recognition of the people of their households, and similarly pigeons have a sense of knowledge and recognition.

Now it is also known that the food one eats is taken into the body of the eater and they become one flesh (see Genesis 2:24). If one were to eat the life of all flesh (Lev. 17:14), it would then attach itself to one’s own blood and they would become united in one’s heart, and the result would be a thickening and coarseness of the human soul so that it would closely approach the nature of the animal soul which resided in that which he ate, since blood does not require digestion as other foods do, which thereby become changed, and thus man’s soul will become combined with the blood of the animal! And Scripture states: Who knows the spirit of man whether it goes upwards, and the spirit of the beast whether it goes downward to the earth?  (Ecclesiastes 3:21). It is for this reason that He (God) said: For as to the life of all flesh, the blood thereof is all one with the flesh thereof (Lev. 17:14), for all flesh, whether man or beast, has its soul in the blood, and it is not fitting to mix the soul that is destined to destruction with that which is to live (in the hereafter).  Rather, it is to be atonement upon the altar to be acceptable before God. This is the sense of the expression Therefore I said to the children of Israel: No soul of you shall eat blood (Lev. 17:12), meaning: “Because the blood is identical with the soul, and it is not proper that one soul devour another, therefore I had compassion upon man’s life and gave it (that is, the animal soul) to him upon the altar, so that the soul of the animal should effect atonement for his soul.”

Thus we have been taught in the Sifre (Parashat Re’eh, piskah 76): “Only be steadfast in not eating the blood (Deut 12:23): R. Yehudah says: (From the fact that it states only be steadfast, which indicates that a special effort was required), you learn that they were addicted to eating blood, etc. For the blood is the life- (Deut. 12:23): this teaches you why it was prohibited. And you shall not eat the life with the flesh- (Deut 12:23):   this prohibits the eating of a limb cut from a living animal.” This is a hint and proof for what we have explained.

It is for this reason that He (God) further commanded us that we are to cover up all blood of an (edible) wild beast or fowl (which have been ritually slaughtered- Lev. 17:13) because their blood is not brought upon the altar, for even of fowls only two species (i.e., young pigeons and turtle doves) may be brought as offerings, and they too are not slaughtered (in the usual way), but in the case of cattle, most of them that are found among men may be slaughtered to the Glorious Name (of God) and their blood is used for atonement, and it is therefore not to be covered. There was no necessity to require the covering of the blood of an ordinary (unconsecrated) animal, since the slaughtering of cattle for ordinary meat was not permitted in the desert, and even afterwards (when the children of Israel came into the Land of Israel and a meal of ordinary, that is, non-consecrated meat was permitted), the commandments of the Torah are directed to the majority (of cases). (That is, since in most cases, cattle were brought as offerings and their blood would be needed for the altar, therefore God did not require covering of the blood even in the remaining cases where cattle were not slaughtered as offerings.)

(I have used the translation found in Charles B. Chavel, (New York, 1974), p. pp. 238-41, with slight modifications.)