PARSHAS ACHREI MOS
"For the nefesh (life-spirit) of the flesh is in the blood, and I have given it to you to atone for you on the altar."
It is taught in the Talmud that once the blood reaches the altar there is atonement. I heard from my teachers that the altar hints to a humble spirit, like the verse says "I build an altar in the brokenness of my heart." This is the main avodah of a person to break the power of strict judgement. Like the verse says, "the sacrifces of G-d are a humble spirit". Because slaying the forces of strict judgement is through a humble spirit. "A broken contrite heart" The main source of haughtiness and bad character traits comes from the blood. It is the strength of the yetzer, this is the meaning of the life spirit of the flesh being in the blood. The Nefesh is the part of the Neshamah that is connected to the blood. It is connected to the Yetzer through the blood vessels. Every time a person fails to purify his blood, through being humble, the blood vessels become heated with the power of the yetzer hara. This is the meaning of the nefesh being in the blood, and I have given it to you to atone for you on the altar. I gave to you the avodah of lifting it up to the altar, by having a broken heart. On the altar, like I built an altar in the brokenness of my heart. This nulifies the power of the heat of the blood that comes from the yetzer hara. Then you will be worthy to atone for your soul. I attone for your souls because the blood is in the nefesh. You will elevate the blood up to the level of soul. Then the blood is in the soul, rather than the soul being in the blood, G-d forbid. Then automatically you will be atoned for through this.
(Divrei Binah - Parshas Achrei p. 59)