The animal-sacrifice, where it has lost its original meaning as an offered gift and has taken on a higher religious significance, has an inner relationship to the hero or god. The animal represents the god himself… The sacrifice of the animal means, therefore, the sacrifice of the animal nature, the instinctual libido.
Jung argues that animal sacrifice, at its deepest symbolic level, enacts the renunciation of instinctual libido, the slain animal being a figure for the god or hero whose death enables psychic and spiritual transformation.
, Symbols of Transformation, 1952thesis