Describe the two primary methods through which a Sadguru accepts service from devotees in the form of books.

According to the preface in Chapter 0, a Sadguru can accept service from devotees through books in two distinct ways. The first method is when the Sadguru creates profound spiritual works themselves, with examples given like Shri Dnyaneshwari or Shri Dasbodh. The second method involves the Sadguru inspiring devotees to write their biographies. The service is then rendered by both the author who writes the text and the wider congregation of devotees who perform devotional study and readings, known as Parayans, of that biography.