Normality and cultural norms
The first major thematic observation of the novel is implicit in the title: the novel will discuss the feelings he feels toward his brother, whom everyone is proud of, who was raised in the Great Depression and helped his family get back on their feet by working hard, unenjoyable jobs. The novel quickly notices that the brother is basically an archetype for his culture. Working hard, pulling one's self up by the bootstraps, and accepting a difficult fate are what traditionally define masculinity in David's Australian culture. The point is that there are subtle assumptions made in each culture that define what a person feels they should do in life.
Writing as a calling
For David, writing wasn't an artistic hobby. First, it was just curiosity. He wasn't satisfied to hear the latest news from third-party sources—he wanted to be in the mix. Then, writing about what he saw became a profession, and suddenly he realized that he was called by nature to be a writer. He has a vocational path, and that separates him from the culture he wants to belong to, but he obeys the higher calling.
Honor and shame
The thing that David talks about but never identifies is shame and honor. He spends a lot of time analyzing the differences between his brother's perception of life and his own. He is a person who is shaped by his desires—his desire to live a special, significant life, his desire to write for acclaim, his desire for achievement. Whereas, his brother is a person shaped by honor, like when he sacrifices for others, when he works hard at jobs that he doesn't enjoy. David feels some shame about not being like his older brother, but the novel itself is a wonderful example of why everyone should just be themselves and accept themselves the way they are, because the novel is an accomplishment that "David" (just the author, thinly veiled) should be proud of.
