According to the preface, how does the act of writing and reading a Guru's biography serve both the author and the wider community of devotees?

Chapter 0 explains that writing and reading a Guru's biography is a profound form of service. For the writer, studying and performing Parayans of a detailed poetic Guru biography constitutes Guru service. For the wider community, when other devotees also study and perform these Parayans, the writer gains the merit of serving God in humanity (Jan-Janardan) and public service. This communal study helps other devotees achieve the purpose of their lives. Essentially, the Sadguru accepts service from his devotees through books, either by writing them or by having his biographies written and then studied by the congregation.