Nature of the Novel
1. The quote in the question refers to the amount of transformations Kurtz had undergone throughout his time spent in Africa. Before readers are introduced to Kurtz, they are already aware of his illness. However as the novel progresses, Kurtz illness becomes more severe and he begins to deteriorate. "His intelligence was perfectly clear ... but his soul had gone mad." This specific part of the quote proves that Kurtz is still intellectually stable, yet his soul had been lost. Conrad is trying to imply that although Kurtz's body is destroyed, his brain remains fine but his soul corrupt. While questing up the Congo River, Kurtz had become the heart of darkness, his soul being corrupt full of evil. "Being alone in the wilderness," this quote is undoubtedly due to the seclusion from society and also civilization. Instead of building friendships and bonds with others, Kurtz felt most satisfied and secure when others feared him.
When Marlow was first encountered with Kurtz, he could not believe the state that this high-class, authoritative man had diminished into. Marlow felt he had "to go through the ordeal of looking into it". Before Kurtz died, Marlow spent a considerable amount of time meeting and conversing with him, sparking a friendship. It is then when those readers realize that Kurtz had not gone mad. For he was trapped in the wilderness, and had merely lost touch with reality, and he had forgotten what it is like to view the world from a civilized perspective.
2. The Climax is reached as readers find out about the death of Kurtz. His final words uttered just before his death were, "The horror! The horror!" Usually people's final words before death are of great meaning. Therefore Kurtz's words were left open for interpretation.