The text mentions studying both knowledge texts like the Dnyaneshwari and Guru biographies. How does the service performed through each type of text lead to spiritual benefits?

The preface in Chapter 0 explains that studying both knowledge texts and Guru biographies constitutes a high form of Guru service. While texts like the Dnyaneshwari are described as purely spiritual and worldly knowledge texts rather than biographies, those who consider the authors or the texts themselves as their Guru perform incomparable, salvation-granting service by studying them. A Guru's biography, on the other hand, is a book detailing the Guru's life, plays (Leelas), and miracles. As Chapter 0 clarifies, the study of such biographies, especially of one's own Sadguru, is presented as the most certain written service for attaining salvation. In both cases, the service is most superior when performed selflessly (Nishkam) for liberation.