The symbol of the unmarried fiancee
Zari's fate comes with symbolic significance because of her role in their small community of friends. Zari was engaged to be married, symbolizing her potential, but Pasha and she were closer and more involved than Zari and her fiance, so she also symbolized the same thing for Pasha who honestly might have had a real shot with her, had fate not intervened. When Zari dies, Pasha sees her everywhere, breaching his own sanity to get closer. When he finally "talks to her" (or Soraya), she says his life still has potential. This is the fulfillment of her role as a symbol for hope and potential.
The Doctor
The human experience evolves with time and experience, but sometimes it is difficult to see far off into the future. That's the problem Doctor solves for Pasha, because he is old enough that Pasha feels a sense of respect for what he says, and he even regards him as a mentor, but Doctor isn't so old that Pasha doesn't relate to him. Therefore, Doctor represents Pasha glancing into his own future to see what fate seems to be handing out to young men in the area these days. And what does he find? He finds that strong, young men in Tehran are kept on a short chain by their government, and any perceived resistance to the government's tyrannical control is met with fatal consequences. Pasha, upon realizing the truth of his situation, loses his mind.
The allegory of the failed launch
At the beginning of the story, Pasha was going to fulfill his dreams in life, and he wasn't letting anything stop him. Throughout the novel though, he finds that some problems, especially political oppression, are so invasive that by no fault of his own, he can be forced to fail. He sees this happening all around him as a part of the oppression, but suddenly, when Doctor is executed, he realizes that it's absolute reality for him, and by the end of the novel, he is not "well-adjusted" as hoped; he is mentally unstable, hallucinating about the dead. This serves as a picture for the brokenness of Iran in the 1970's, the way the government affected the lives of its citizens. Instead of helping its citizens to accomplish a better life, the government intentionally clipped people's wings, eliminating their hope.
The United States
In this book, the United States of America is a symbol for an alternative life to the Iranian experience of life. By encouraging Pasha to continue his journey toward film school in America, Zari is saying, "Things can change. If you can get out of here, life can be better for you." This is especially powerful the last time they speak, when Pasha sees Zari in Soraya and speaks with her. She urges him to keep trying to get out of Iran.
The minor characters as symbols
Not only is Pasha simultaneously interested in Doctor and Pasha, but also, when Pasha and Soraya meet later, he thinks she is also Zari somehow, meaning that of the 6 characters in the book, one couple married, one couple died, and the remaining couple had ties to both the living and the dead. This balance is likely intentional, and since Pasha and Doctor's interest in Zari never leads to any conflict, it might be interesting to view them as two parts of one person. In that case, Doctor's death would coincide with the death of Pasha's childish hope.
