Can you explain the two ways a Sadguru might accept service from devotees through books?

According to the preface in Chapter 0, a Sadguru accepts service from devotees through books in two primary ways. The first is when the Sadguru is a great author themselves, creating profound works like the Shri Dnyaneshwari or Shri Dasbodh. The second method involves the Sadguru inspiring devotees to write their biographies. In this case, the writer performs a service by creating the work, and the wider community of devotees performs a service by studying it and conducting Parayans (devotional readings). This allows both the writer and the readers to engage in service and fulfill the purpose of their lives.