Based on the preface, what are the two distinct ways a Sadguru can offer service to devotees through literary works?

The preface, in Chapter 0, outlines two principal methods by which a Sadguru provides service through books. The first method involves the Sadguru creating monumental spiritual works themselves, with examples given like the 'Shri Dnyaneshwari' or 'Shri Dasbodh'. The second method is when the Sadguru has their biographies written by their devotees. In this case, the Guru accepts service from both the writer and the congregation of devotees who engage in the study and ceremonial reading (Parayans) of the biography. The 'Shri Sai Satcharita' itself is a prime example of this second form of service.