What are the different ways a Sadguru accepts service from devotees through literary works?

According to the preface in Chapter 0, a Sadguru accepts service from devotees through books in two distinct ways. The first is when the Sadguru themselves authors great spiritual works, with examples like Shri Dnyaneshwari or Shri Dasbodh. The second method involves the Sadguru having their biographies written by their devotees. In this case, the Guru accepts service from the writer who creates the biography and also from the broader congregation of devotees who then perform study and Parayans (devotional readings) of that work, thereby helping them achieve their life's purpose.