What are the two primary ways a Sadguru receives service from devotees through literary works, as described in the texts?

According to the preface in Chapter 0, a Sadguru accepts two main types of service from devotees through books. The first is when the Sadguru creates great works themselves, such as the Shri Dnyaneshwari or Shri Dasbodh. The second method is when the Sadguru has their biographies written by their devotees. In this case, the Guru accepts service from the writer, and also from the wider congregation of devotees who engage in the study and devotional reading (Parayans) of that biography. This act of collective reading and study is considered a vital form of service.