As Good an Explanation As Any

One day, the cat caught the mouse but refrained from eating it or even killing it.
"Is this mercy? The world is different from what I thought and what it must be. Rather, do you eat me forthwith." That was what the mouse said. The cat resisted the injunction. "As to how the world is, I know nothing of it, but I am aware of mice and that you are the god of them. Don't think I can be fooled. If I kill you, your godhead, freed from your tiny body, can easily take possession of my superior frame. Then you will be better positioned to do good for mice. Well, I have no opinion on whether mice should fare better or worse, but it goes against my sense of aesthetics that a god should not be the thing of which it is the god."
"I hesitate to disturb your composure, but I must say that many gods violate your precept even today."
"I know it. The discomfort causes me to screech, to yowl, to scratch surfaces unaccustomed to rough treatment. My entreaties have had no result. Shall I contribute myself to what I abhor? If the winners offered a reward perhaps, but not under any other circumstance." The cat spoke thus and, no longer interested in the mouse god, removed itself from the scene.
The mouse god therefore squeezed into a hole and found a crack that led down, down to the core of the planet. It died there. Just as the cat understood, the godhead swelled and inspirited the entire planet. Getting rid of all mice has been an impossibility since then, for the world itself watches over them.
Finis