The moral lesson implicit in Jack London's short story "To Build a Fire" is a stern and cheerless one. It might be expressed as follows. Man is alone in a pitiless, godless universe. He cannot look to any supernatural power for any kind of assistance. The best thing that humans can do because of their mutual human predicament is to cooperate and work together to make existence as comfortable and secure as is possible. But in the long run we are all doomed to the same extinction that occurred to the unnamed protagonist of London's story. Jack London was a socialist, and his story has a socialistic as well as an atheistic theme. London might also be called an existentialist, but he lived long before that term was coined by the French philosopher Jean-Paul Sartre.
The story calls to mind "The Open Boat" by Stephen Crane, as well as the essay by Sigmund Freud titled "The Future of an Illusion." Crane and London both resemble the pessimistic author Ambrose Bierce, whose best-known story, accessible in e-notes, is "An Occurrence at Owl Creek Bridge." The same theme can be seen in a number of Ernest Hemingway's stories, most notably in "A Clean, Well-Lighted Place." Jack London's stark, fatalistic view of life might well be summarized by quoting this very short poem of his contemporary Stephen Crane.
A man said to the universe:
“Sir, I exist!”
“However,” replied the universe,
“The fact has not created in me
A sense of obligation.”