The panther is established as the artist's polar opposite. Whereas the artist is frail and lacking in any kind of desire, the panther is energetic and hungry for meat. The artist is associated with death due to his skeletal appearance. The panther is filled with life.
The artist fasts because he seeks to attain spiritual perfection through his art. He lives in constant hunger for this purpose—or so he would have it appear. Later on, he reveals that the only reason he fasts is that he could never find any food he enjoyed; he has no zest for living, in other words, nor does he have true spiritual fulfillment. In the end, he is alienated from both the physical and spiritual world.
The panther is filled with life, desiring food and projecting an aura of liberty even within the confines of a cage. The panther's relish for meat and its physical power link it to the material world. In the material world, the panther finds contentment and an audience eager to watch him. Though he is a prisoner, he is still better off than the artist, cut off from nourishment, pleasure, and communal adoration.
So taking the characterization of the artist and the panther in mind, it can be said that the panther represents the only alternative to a spiritually dead world: mindless indulgence and enjoyment of the senses.