How does the preface distinguish between worldly and spiritual Guru service, particularly in the context of writing biographies?

The preface makes a clear distinction between worldly and spiritual service. Writing biographies of great worldly figures like politicians or historians is considered a worldly service. While it may have educational value, it is limited by time and space and is often rooted in self-interest, thus not yielding spiritual fruits. In contrast, as detailed in Chapter 0, writing the biography of a saint or one's Sadguru is a form of spiritual service. The highest form of this service, writing about one's own Sadguru, is said to grant the ultimate fruit of salvation.