There are two ways that the idea of ‘Christopher’s book’ functions.
Firstly, the writing of the book directly conveys Christopher’s attitudes and feelings towards his life - almost like a diary. It teaches us about his unique perspective on the world. Although he tells us it’s a murder mystery novel, it reveals a lot about him and his emotions. For example, Christopher’s frequent asides about the natural world or physics - such as the growth of frog populations - reveal his love for the logical, scientific, and rational. He enjoys order and rules and struggles to understand and cope with things that are disorderly, emotional, or illogical - like when his father tells him his mother died of a heart attack. His reaction is to ask what kind of heart attack. He more distracted by the lack of logic - she was too young to die of a heart attack - than the emotional impact of her death. By explaining Christopher’s thinking and motivations, his book helps the reader to empathise with him.
Christopher’s book also functions to show societal attitudes and Christopher’s response to them. This teaches us more about him and his feelings and attitudes towards life. For example, he describes his father’s habit of putting his pants on before his socks. The way that he describes points out the eccentricity of this behaviour. In comparison, much of Christopher’s behaviour seems very normal. The book exposes that there is no real difference between him and to so-called ‘normal people.’ By showing us the world through his eyes, Christopher’s book helps us see that everything is subjective.