How does a Sadguru, like Sai Baba, receive service from devotees through literary works?

According to the preface in Chapter 0, a Sadguru accepts service from devotees through books in two primary ways. The first is by creating profound works themselves, such as the Shri Dnyaneshwari. The second method, more relevant to devotees, is by having their biographies written by their followers. These devotees, like Annasaheb Dabholkar who wrote the Shri Sai Satcharita, provide a service through the act of writing. Further service is accepted through the subsequent study and Parayans (devotional readings) of these biographies by the wider congregation of devotees, allowing many to achieve the purpose of their lives.