Describe the different types of Guru service discussed in the preface and how they are valued.

The preface, as detailed in Chapter 0, outlines several forms of Guru service. The first is worldly service, such as writing biographies of politicians or jurists, which is considered limited by time and space and rooted in self-interest, thus not yielding spiritual fruit. A higher form is writing the biographies of many saints, which is a form of spiritual service but is still considered partial. The best and most certain service for salvation is described as writing the biography of one's own Sadguru with a pure heart and unwavering devotion, and then regularly studying it through recitations.