The writer uses irony to demonstrate Winston's point of view.
The technique that the writer uses as the excerpt closes in order to demonstrate Winston's point of view is irony. The passage describes Winston's initial belief that the girl who gave him the note is an agent of the Thought Police, but then considers the wild possibility that the message came from an underground organization and that the girl is part of it.
The ironic twist comes at the end when Winston reads the message on the paper, which simply says, 'I love you.' This contradicts his initial fears and raises the hope that the message may not mean death as his intellect tells him, but rather represents a different kind of message altogether.