What are the two types of service a Sadguru receives from devotees through books?

Chapter 0 outlines two distinct ways a Sadguru takes service from devotees through literary works. The first is when the Guru themselves authors profound spiritual masterpieces, with Shri Dnyaneshwari and Shri Dasbodh cited as examples. The second form of service occurs when the Sadguru has his life story written by his followers. The service is then rendered by the writer through the act of creation and by the larger congregation of devotees who perform study and Parayans of the completed biography, thus engaging with the Guru's life and teachings.