When it begins to get cold, Thoreau builds his chimney out of bricks and sand and stones and mortar, and he plasters the walls of the house to keep the wind out. He gathers some nuts and fruits more for their beauty than for food. He says that sometimes he dreams of a larger house, although in society it is the custom to invite a guest to your home, keep them at the greatest distance from you while inside, and call it hospitality. He would rather be close to his guests.
The work of preparing his house for winter is enjoyable for Thoreau and reinforces his spiritual connection with nature. Civilized man's desire to have a big house in which to entertain guests ironically keeps him from actually interacting with them.
The first ice that forms over the pond, Thoreau says, is hard, dark, and transparent, and through it he studies the bottom of the pond and the bubbles in between the ice. He marks the date it first snowed and the date the pond freezes over completely. He takes pleasure in the work of collecting firewood, one of the commodities that society values that even he cannot do without. Normally he leaves his fire burning in the house while he is gone, though once his bed linens caught fire. Luckily, he extinguished them before major damage was done. He likes to look into the fire and says you can always see a face there.
Nature is Thoreau's companion. He observes it closely and, when it drives him inside, he appreciates its rhythms, respects its power, and finds company even in the fire. Firewood, and the warmth it gives, is a necessity, so Thoreau shares his need for it with those who live in society.