The preface mentions two key services a Sadguru receives through books. Could you explain these and how they relate to building a following?

The preface in Chapter 0 outlines two distinct ways a Sadguru accepts service from devotees through literary works, which in turn helps cultivate a community. The first method is when the Guru creates a great work themselves, such as the Shri Dnyaneshwari. The second method, which is highly relevant to Sai Baba, is when the Guru has their biography written by a devotee. This biography then becomes a focal point for service from both the writer and the entire congregation of devotees through study and Parayans. The Shri Sai Satcharita, written by Annasaheb Dabholkar, is presented as the primary example of this second form of service, providing a foundational text for devotees to gather around and study together.