The forest
The forest appears in the beginning when Sophie returns home from school. The forest is described as being a dense one, hard to navigate through if a person is not familiar with it. The forest is also used here as a symbol to make reference to the struggles someone who is growing up has to face and how hard it is to navigate through those feelings and emotions.
Safe space
A place where Sophie feels protected is the hedge where she goes shortly after discovering the letters. She hides there while she reads them and then she remains there for a while, pondering about the meaning of the letters. The hedge resembles a womb and thus it is used here as a symbol for a safe space.
Way of explaining the world
A common motif in the novel is the idea that mythology was used in the past as a way of explaining the world. Whenever someone in the past encountered something they were unable to explain, they tried to make sense of it by creating a story around it and by attributing the event to some God or another. Thus, mythology is considered by the anonymous philosopher and by Sophie as an early attempt to explain the world.
Symbol for civilization
When Sophie and the anonymous philosopher talks about ancient civilizations, they mention the art and large cities that were often associated with ancient societies like the Greek one. These elements are used here as a symbol for civilization and are used to suggest the presence of an advanced country.
Gold crucifix
In the novel, various characters have gold crucifixes which are considered as being a symbol for Christianity and religion in general. When a character loses however their gold crucifix, this symbolizes the fact that the person in question lost its faith and no longer trusts religion in general.