BASED ON: Rabbi Pinches Friedman - Aharon: Your Contribution Is Superior to Theirs - By Lighting the Menorah Aharon HaKohen Was Tasked with Restoring the Light of Hashem— the Neshamah —to the Body of a Sinner 

At the time of the transgression, the sinner is

categorized as a “beheimah” rather than an “adam.” After

performing teshuvah, he returns to the status of “adam.”

Therefore, he no longer deserves to be sacrificed as a korban;

instead, he is permitted to substitute an animal as a korban.

Regarding the question as to what sin did the animal commit,

we refer to the words of the Arizal. Within the sacrificial

animal is the gilgul of a “rasha,” who requires tikun for the very same transgression as the person offering the korban. Furthermore, we learned from the Yismach Moshe that when he sacrifices the animal, he is actually sacrificing a part of himself, because his tainted soul actually becomes part of the korban.