What is the author's central or main idea in "To Build a Fire"? Please explain.

I feel that a theme (main idea) of London's "To Build a
Fire" is a theme that he frequently uses in his writings.  That theme is the theme of
nature's indifference to humans.  Granted, the man ignored advice to not go out, because
he figured he was good enough, strong enough, and smart enough to conquer nature.  That
wasn't the case, and the man paid the ultimate price.  I would be tempted to believe
that the main idea being stressed to readers is "be prepared," but the dog ruins that
for me.  

Then
it turned and ran along the trail toward the camp it knew, where there were the other
food providers and fire
providers.

For me, the dog
represents nature.  The dog is not human; therefore, he is nature to me.  The dog sticks
around for a bit after the man dies, then the dog simply moves on in search of other
providers.  I feel that this shows a cold indifference on the dog's part.  He liked the
man, as long as the man could provide something for him.  The storm is a lot like the
dog.  It exhibits a sense of cold indifference to the man's efforts.  It doesn't matter
how hard the man tries to warm himself and curse at the storm.  The storm simply carries
on without a care in the world.  The story has always reminded me of Crane's poem "A Man
Said to the Universe."

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A man said to the
universe:

“Sir, I
exist!”

“However,” replied the
universe,

“The fact has not created in
me

A sense of
obligation.”

In the poem,
like in London's story, nature flat out doesn't care about man and his efforts.