The second and third sections are important because they relate the progress of Marlow’s journey upriver into the heart of darkness. Section II emphasizes the physical voyage on the boat moving up the river until he reaches Kurtz’s station, while Section III tells of his meeting Kurtz, efforts to understand what has befallen the man, and final efforts to make sense of the entire journey.
In Section II, as Marlow moves upriver and approaches the station, he learns more about Kurtz and the effects of the illness he had suffered. The physical aspects of the journey grow increasingly difficult. Sometimes the river is nearly impassable, and the African “cannibals” must push the boat. Farther upriver, surrounded by forest and a dense fog, unseen assailants shoot arrows at the boat, killing the helmsman. Everyone on the boat assumes Kurtz is dead, but when they finally reach the station, the Russian manager emerges; the native attackers were trying to protect Kurtz, who is still alive.
In Section III, Marlow finally meets Kurtz and sees the macabre spectacle he has made of his camp, with decapitated heads atop wooden posts. Obviously quite ill, Kurtz is emaciated and weak. At first well spoken, he soon makes little sense to Marlow, who tries to persuade him to leave immediately for Europe. Kurtz soon dies, after handing over his report on “Suppression of Savage Customs.” Marlow stops in Brussels on his way back to England. In the report he reads Kurtz’s terrifying recommendation, “Exterminate all the brutes.” Marlow can neither forget Kurtz’s dying reflection on “the horror” nor conclude if he referred to what he had seen or what he had done. The horror or darkness will unquestionably stay with Marlow.