Milne apparently had some sort of personal revelation prior to writing this essay. His attitude toward winter has dramatically changed. Instead of a "horrid," "dreary" season, he now can see "sparkling days, long pleasant evenings, cheery fires."
He also has a new resolve: Good work shall be done this winter. Life shall be lived well. This implies that good work has not been done in winters pasts and that the author's winter months had been subpar. Milne writes that he had "forgotten" what it was like to face winter with "calm." So he once knew this feeling but had somehow gotten so far away from it that the opposite had become true. In this sense, he is returning to an earlier time in his inner life.
What can the reader learn about Milne from this essay? Think of adjectives that describe his new attitude about winter and adjectives that describe his old attitude. Also, consider that Milne is deeply examining his life, writing about it, and adjusting his attitude. What adjective(s) describe people like this?