What are the two primary ways a Sadguru accepts service from devotees through books, and how does this foster a following?

According to the source material in Chapter 0, a Sadguru takes two forms of service from devotees through books. The first is by creating profound works themselves, such as the Shri Dnyaneshwari. The second method, which directly fosters a following, is by having their biographies written by their devotees. The Sadguru then accepts service in the form of study and Parayans from both the writer and the wider congregation of devotees. This shared practice of studying a detailed biography, like the Shri Sai Satcharita, helps build a community dedicated to the Guru's life and teachings.