Describe the two primary ways a Sadguru might receive service from devotees through literary works, as explained in the preface.

According to the preface detailed in Chapter 0, a Sadguru accepts service from devotees through books in two principal ways. The first method is when the Sadguru creates profound spiritual works themselves, with examples given like Shri Dnyaneshwari or Shri Dasbodh. The second method, which applies to the Shri Sai Satcharita, is when the Sadguru has their biographies written through their devotees. In this second form, the Sadguru accepts service both from the writer who composes the biography and from the wider congregation of devotees who engage in its study and perform Parayans, thereby fulfilling the purpose of their lives.