How does the preface distinguish between worldly Guru service and spiritual Guru service?

The preface in Chapter 0 makes a clear distinction between worldly and spiritual Guru service. Worldly service, such as writing biographies of public figures like politicians or historians, is acknowledged as a form of public service. However, its importance and fruit are not eternal, being limited by space and time. Furthermore, it is often rooted in self-interest and therefore does not yield spiritual benefits. In contrast, spiritual service, such as writing the biography of a saint or one's Sadguru, is aimed at attaining spiritual fruits, with the ultimate goal being salvation. This type of service, especially when performed selflessly (Nishkam), is considered superior and spiritually potent.