Without knowing the specific text or author you are referring to, I cannot give you a specific answer. However, in general, authors may use different pronouns to achieve different effects or to connect with their readers in different ways. Using the second person "you" can create a sense of intimacy and directness between the author and the reader, while using the first-person plural "we" can create a sense of shared experience or community between the author and the reader. The author may have switched to the first-person plural in order to include herself or himself in the discussion, or to create a sense of shared interpretation with the reader.