Komentarz do Kapłańska 9:9

ואת הדם יצק אל יסוד המזבח, “and he poured the blood upon the foundation of the Altar.” He did this in order to achieve atonement for man whose existence is dependent on blood. This is the meaning of Leviticus 17,14: “for the life-force of all flesh resides within its blood.” It is also written (Leviticus 17,11) “for he atones for the blood which resides in the נפש, ‘life-force.’” This then was the reason that the High Priest was burning up the following three items, “the fat parts, the kidneys, and the tissue attached to the liver.” All of these parts of man had to partake in order for the sin to be carried out (golden calf) and they were instrumental in turning the people away from the path of goodness to the path of evil. This is the deeper meaning of “and the fat-parts, the kidneys and the tissue adjoining the liver of the animal which was the sin-offering he made go up in smoke on the Altar” (verse 10). The part called חלב is the fat which causes man to become gross, arrogant; it is responsible for man’s inherent pride and arrogance. Moses alluded to this when he said (Deuteronomy 32,15) “Yeshurun grew fat and kicked, you became fat and gross and coarse;” we also have a verse in Job 15,27 depicting something similar: ”his face is covered with fat and his loins with blubber.” [The speaker refers to a king rebelling against the Lord. Ed.]
The kidneys are the source of what is called עצה, “counsel,” in the language of our sages (Berachot 61); they base this on Psalms 26,2 “ונסני צרופה כליותי ולבי, “and try me, test my heart and kidneys (mind).” Another verse (Psalms 16,7) carries a similar message, i.e. אף לילות יסרוני כליותי, “my kidneys (conscience) admonish me at night.”
The reason the tissue adjoining the liver had to be burned up is that desire, carnal and other kinds of greed which permeate man, have their origin in that region of the body. It is also the region which is the (physical) cause of anger and rage. All the negative virtues in man are connected to the liver. All of these parts the Priest burned up in the northern part of the Altar as the north is the region from where all evil originates, (compare Jeremiah 1,14). In other words, evil is consigned back to where it originated (symbolically speaking). All these procedures have one purpose, to achieve atonement for man’s sins which originate in the fatness of his heart and the planning of his ego which originates in the liver.