How does the Narada Purana describe the two types of service a Sadguru takes from devotees through books?

The provided text does not state that the Narada Purana describes the two types of service a Sadguru takes from devotees. Chapter 0 mentions two separate points. First, it references the Narada Purana to establish that the service of writing a Guru's biography is an ancient practice. Second, in a different section, it states that a Sadguru takes two types of service from devotees through books, but the provided excerpts do not elaborate on what these two types are. The text does, however, discuss using texts for 'Kamya' (with desire) and 'Nishkam' (selfless) purposes.