Based on the provided text, what are the dual benefits of writing and studying a detailed biography of a Guru?

The text outlines a significant two-fold benefit that arises from the creation and study of a detailed poetic Guru biography. As explained in Chapter 0, when an author writes such a work, they are performing a direct form of Guru service. At the same time, a secondary benefit is realized when other devotees study this work and perform Parayans. In this case, the writer gains the additional merit of serving God in humanity (Jan-Janardan) and performing public service, while the devotees who study the work are also able to achieve the purpose of their lives.