From the perspective of the author, what is the dual purpose of writing a Guru's biography, according to the provided text?

According to the preface in Chapter 0, the author of a Guru's biography serves a profound dual purpose. Firstly, by undertaking the effort to study and write a detailed poetic biography, the writer is performing a direct form of 'Guru service.' Secondly, and just as importantly, the author's service extends to the wider community. As Chapter 0 explains, when other devotees study and perform Parayans of this biography, the writer gains the merit of 'serving God in humanity (Jan-Janardan) and public service.' This is because their literary creation becomes a vehicle through which other devotees can connect with the Guru and 'achieve the purpose of their lives,' thereby benefiting the entire congregation.