“Outside the camp” is a location where the defiled and unclean are placed. For example, the dwelling place of a leper was “outside the camp” (Leviticus 13:46), a man who was charged with blasphemy against the Lord was stoned to death “outside the camp” (Leviticus 24:14). Likewise, the unclean parts of the animal are taken there because they are unclean and impure (Leviticus 4:11–12). Ross (p.132) suggests that the ritual of the sin offering revealed the contagious nature of sin, especially since it affected the Holy Place. As the sacrifice was infected by sin, it had to be burned outside the camp, the place of uncleanness. This act signified the complete removal of impurity.
12 all the rest of the bull he shall carry outside the camp to a clean place, to the ash heap, and shall burn it up on a fire of wood. On the ash heap it shall be burned up.