According to the preface, in what ways does a Sadguru accept service from devotees through books?

The preface in Chapter 0 describes two primary ways a Sadguru takes service from devotees through literary works. The first method is when the Sadguru creates great spiritual works themselves, such as the Shri Dnyaneshwari or Shri Dasbodh. The second method involves the Sadguru having their biographies written by devoted followers. In this case, the Sadguru accepts service from the writer who creates the biography and also from the congregation of devotees who engage in its study and perform Parayans (devotional readings) of the text.