The Garden
The Garden is a symbol in the novel because it is a Biblical allusion to the Jewish creation myth. According to the book of Genesis, human beings started in a garden (and also, this motif appears throughout world mythology with similar ideas). The allusion symbolizes a transition from innocence to a broken world through sin and brokenness. In this case, the loss of garden community is a clear reference to the Holocaust.
Alberto, the foil
The narrator experiences survival's guilt about being spared from the horrors of the Holocaust. This makes his consideration of Alberto highly symbolic. By empathizing with his foil, he is asked to consider the truth about his own human life, the likelihood of suffering, the absolute finality of death, and the strange quality of fate that would allow something this horrible to happen. Put simply, Alberto symbolizes his existential crisis about death caused by the Holocaust.
Micol, the unrequited love
Micol is also a symbolic character. She symbolizes an archetypal quality of the narrator's experience, and when she dies, she symbolizes the full weight of mourning and love lost. The archetypal quality can be seen because she rejects the narrator when he proclaims his love for her. In some literature, this archetype comes through as a "femme fatale." She is the Anima archetype, because she signals the self-esteem crisis within the narrator, causing him to become completely obsessed and enamored. But in the end, her death signals something more complex, that because of her untimely death in a concentration camp, she symbolizes to the narrator that the nature of suffering extends far past his own emotional interests. The loss is unfathomable.
The tennis club
This attempt to form community is symbolic. It comes in the aftermath of new, hateful legislation making it illegal for Christians and Jews to hang out. The club comes with an invitation to the community to stay close. The tennis aspect involves the idea of competition into the mix, pointing to the competitive nature of the rift. The symbol shows that competition doesn't have to sever community, raising this question: Why should community ever be separated just because of diversity or differences in religious opinion?
The horrors of the Holocaust
The symbolic consideration of the novel is the Holocaust, because that is the "fall" that makes the community descend into chaos and brokenness. The child is so damaged by these events that, without ever explicitly depicted what the people went through (probably because the child never had to see it, so his narrative doesn't contain that), the reader knows that the Holocaust has caused a shudder of horror to spread into every community in Europe and beyond. The Holocaust is like a bomb, and this young narrator is stuck in the aftershock, trying to figure out why he should care about something as trivial as math class in light of such agonizing events.
