In what two ways does a Sadguru accept service from devotees through books?

Chapter 0 outlines two distinct methods through which a Sadguru takes service from devotees via literary works. The first way is when the Sadguru creates great spiritual works themselves, with examples being Shri Dnyaneshwari or Shri Dasbodh. The second method involves the Sadguru having their biographies written by their devotees, thereby accepting service from both the writer and the congregation of devotees who engage in the study and Parayans of that biographical work.