Cats are intended to teach us that not everything in nature has a purpose.

Keillor’s line uses the domestic cat as a comic emblem of nature’s indifference to human ideas of utility. Cats often appear to act for their own pleasure—sleeping, prowling, ignoring commands—so they puncture the comforting belief that everything exists “for” something else. The quip gently satirizes purposive or moralizing views of the natural world (and, by extension, of human life), suggesting that some things simply are: self-contained, aesthetically complete, and not accountable to our need for meaning. Its humor depends on recognizing cats as both familiar companions and stubbornly uninstrumental creatures, inviting a more relaxed, less teleological way of looking at existence.