What are the two forms of service a Sadguru receives from devotees through books, and how does this contribute to a legacy?

Chapter 0 outlines that a Sadguru takes two types of service from devotees through literary works. The first is when the Sadguru creates great works themselves, like the Shri Dnyaneshwari. The second, more common for devotees, is when the Sadguru has their biographies written by followers. The service is then accepted from both the writer and the congregation of devotees who perform study and Parayans of the work. This process leaves the world in debt to these devotees, as it creates a lasting, detailed record that allows future generations to connect with the Guru, ensuring the teachings and life story endure.