The lines suggest that the narrator is experiencing a sense of disconnection from their own identity. The fact that they see a face in the small rectangle, but do not recognize it as their own, indicates a feeling of alienation or dissociation from themselves.
This creates an eerie, unsettling feeling for the reader and adds a layer of mystery to the section. The lines contribute to the development of the section by building tension and creating a sense of unease. They also hint at a deeper psychological or existential struggle that the narrator may be experiencing. Overall, these lines add complexity to the narrative and create a sense of intrigue that draws the reader in.
I haven't read this book but this is my assumption.