Humans are diverse and beautiful.
The first and foremost argument that this book offers is the idea that all humans should have complete freedom to define their identity as they see fit, because when everyone lands on their "official" identity, the picture of all the humans is rich and diverse, and people feel that their identity is meaningful.
But, too often, we perceive each other in blanket assumptions, like "All Muslims are like this," or "All Christians are like that," and then that diversity doesn't make sense anymore. According to Yusef's story, we should be socially open-minded, regardless of our religious or political views, if we want to understand the value of diversity.
Islam is countercultural, like punk.
There is a clever song lyric that wins the prize for "Most thematic sentence in the novel." The idea is simply this line: "Mohammad was a punk rocker." Although the idea is certainly offensive to conservative Muslims, the comparison is actually quite savvy. In the West, Christianity sets the tone for default, normal culture, at least historically, so both punk culture and Islamic culture are about reminding the majority that people are beautiful in their diversity and individuality.
In other words, Muslims understand what it's like to be radically misunderstood by the majority, so just like delicate people might cringe at the sight of a real punk person, many people become hostile or nervous when Muslim people are present. At least in this book, hey are similarly mistreated people groups.
Cultivating open-minded communities with similarly thinking people.
This theme is a bit of a juxtaposition; the novel argues clearly that Yusef was not happy in the would-be communities of his college dorms. He felt like he wanted to belong somewhere, where his way of life was considered more standard, so people could know him better.
However, Yusef didn't guess that his life in community with Muslims would be so diverse. But, since the diversity of the group didn't come between their shared cultural values and their love for the Koran as they understand it, they were able to quickly bond, trusting that they were with like-minded people (even when their interpretations of the Koran vary drastically. Look at Umar and Rabeya's theologies, for instance—they're nearly opposite.
