What are the two primary ways a Sadguru is said to receive service from devotees through books?

Chapter 0 outlines two distinct methods through which a Sadguru accepts service from his devotees by means of books. The first way is when the Sadguru authors great spiritual works himself, with the text providing examples such as the Shri Dnyaneshwari or Shri Dasbodh. The second method described is when the Sadguru has his biographies written through his devotees. In this scenario, he accepts service from both the writer of the biography and from the larger congregation of devotees who engage in the study and devotional reading, or Parayans, of that work.