What does the preface say about the nature of Guru service?

According to the preface, Guru service can take many forms, including both worldly and spiritual actions. It references Lord Dnyaneshwar Maharaj, who taught that serving saints with one's entire being is the doorway to knowledge. The text explains that writing biographies of great worldly figures is a form of public service, but it is limited and does not yield spiritual fruits. Conversely, writing the biographies of saints is a form of spiritual service. As detailed in Chapter 0, the highest service is writing the biography of one's own Sadguru with pure devotion.