The text mentions two types of service a Sadguru takes through books. Can you explain them in relation to Sai Baba?

The preface, as detailed in Chapter 0, explains two ways a Sadguru accepts service via books. The first is by creating great works themselves, like the Shri Dnyaneshwari. The second is by having their biographies written by devotees. Sai Baba's case falls into the second category, where he accepted service through his devotee Annasaheb Dabholkar, who wrote the Shri Sai Satcharita. The service is then extended to the entire congregation of devotees who engage in study and Parayans of this biography.