According to the preface, what is the role of literature like the Shri Sai Satcharita in serving the Guru and the community?

The preface in Chapter 0 explains that a Sadguru takes two types of service through books. One way is by having his biographies written by devotees. These books then serve a dual purpose. For the writer, it is a form of Guru service. For the wider community, studying and performing Parayans of the work becomes a way to serve God in humanity (Jan-Janardan) and is considered public service. The Shri Sai Satcharita, written by Annasaheb Dabholkar, is presented as the definitive, detailed work for Sai devotees to engage in this form of service, thereby strengthening the community and helping individuals achieve the purpose of their lives.