How does a Sadguru engage devotees through literary works?

According to the preface, a Sadguru takes two primary forms of service from devotees through books. As detailed in Chapter 0, the first is by creating profound spiritual works themselves, such as the Shri Dnyaneshwari. The second method is by having their biographies written by devotees. These biographies, like the Shri Sai Satcharita, are then accepted as a form of service through study and Parayans (devotional readings) performed by both the writer and the wider congregation of devotees, allowing many to achieve the purpose of their lives.