The source mentions two types of service a Sadguru takes through books. How does this relate to spreading Sai Baba's legacy?

Chapter 0 explains that a Sadguru accepts two kinds of service from devotees via books. The first is by creating great works themselves, and the second is by having their biographies written by devotees. Sai Baba's legacy is spread through the latter method. Devotees like Annasaheb Dabholkar wrote the Shri Sai Satcharita, a detailed and inspirational biography. The Sadguru then accepts service from the writer and the congregation of devotees through the study and performance of Parayans of this work. This process of writing, studying, and collectively reading the biography is a key method for preserving and spreading his teachings.