What is the authors purpose for leftovers and tracers

It's to know your purpose before you read something because a purpose can:

Which statement correctly describes the verb function in this sentence? the word “dancing” is a verb that functions as a noun. the word “dancing” is a verb that functions as an adjective. the word “becoming” is a verb that functions as a noun. the word “becoming” is a verb that functions as an adjective.

London includes a quote about john thornton as he is observing hal attempt to motivate the exhausted dogs "it was idle, he knew, to get between a fool and his folly". if the word "idle" is defined as "of no real worth, importance, or significance", what does this statement mean with regard to hal? who is the fool? what is hal's folly? why would john thornton think it of no real worth or useless to intervene?