"Aaron approached the altar and slaughtered the calf he had for a sin-offering." (Levit. 9:8)

This verse alludes to a conversation in the celestial spheres which is reported in the Jerusalem Talmud: (Makkot 2:6) "They enquired from ‘Prophecy’: what shall be the punishment of a person who has sinned? Answer: ‘The soul (person) who sins, she (the soul) will die'. (Ezek. 18:4)

...Aaron...readied himself to place his own soul on the altar as a guilt offering.

When they asked ‘Mercy’ the same question, the answer given was: ‘he shall bring a sacrifice’." The major factor determining the value of the animal sacrifice is the thoughts it evokes in the person offering it. If that person will realize that everything which is being done to the sacrificial animal is something that should really be done to him, the offering may affect atonement for its owner. When the Torah writes that Aaron approached the altar this is another way of saying that he readied himself to place his own soul on the altar as a guilt offering. He was aware that when he performed the act of slaughtering the animal, this was an act of mercy by G‑d who spared his life and allowed him to present the animal’s life as a substitute for his own.

In order to understand the system of crime and punishment and the apparent ease with which atonement can be obtained by the offering of an animal, we must consider various statements by our sages. Tanchuma Shoftim posits that G‑d has sworn to hold the universe and the creatures therein responsible for their deeds. "If anyone were to declare that G‑d is an indulgent and lenient G‑d, he will experience that his bowels will become loose" (Jerusalem Talmud Shekalim 5:1) (The Hebrew words for ‘indulgent’ and ‘loose’ are quite similar in this verse.) If, as the prophet said (Ezekiel 18:4) the sinner ought to die for his sin, how is it that he only has to offer a sacrifice in order to escape death?

I believe we can find a reason for this which is acceptable even in legal terms. At the time a person commits a sin he does not do so as a human being in full command of his faculties. Rather, he has temporarily taken leave of his senses or he would never have committed the sin in the first place.

...he will realize the anguish the beast suffers when it has to die...

Compare Sotah (3), where we are told there that prior to committing a sin man’s mind is afflicted by some mental disturbance. Had the person committing the sin not descended to a spiritual level such as that of a beast he would not have committed the sin. On the day such a person becomes a penitent, his soul has reasserted itself and he again assumes the spiritual level of a human being. Would it be fair to kill such a human being because of what he did while he was on the spiritual level of a beast? When such a person has to offer a beast in expiation of his sin he will realize the anguish the beast suffers when it has to die, and he will appreciate that he himself had been in a situation similar to that of the best which now has to die. Man’s sensitivity to the animal’s anguish then is what really saves him from the fate of the animal.

This is what the Psalmist has in mind when he speaks of "man and beast, You deliver, O L-rd". (Psalms 36:7) G‑d has delivered the part of man which is similar to the beast because man chose to allow his spiritual part to dominate him. His spiritual part had not deserved to be punished as it had no part in his sin. When looked at from this point of view the requirement to bring this sacrifice is part of justice as opposed to being in lieu of justice. This is why the Psalmist introduced the verse we quoted by saying: "Your justice is like the great deep."

[Selected with permission from the five-volume English edition of "Ohr HaChaim: the Torah Commentary of Rabbi Chaim Ben Attar" by Eliyahu Munk.]