What are the different types of 'Guru service' discussed in the text, and how do they compare in terms of spiritual benefit?

The text outlines several forms of Guru service, distinguishing between worldly and spiritual types. As mentioned in Chapter 0, one form is writing biographies of great worldly figures like politicians or historians, which is considered a public service but is limited by time and space and does not yield spiritual fruits because it is often rooted in self-interest. A higher form of service is writing the biographies of many saints, which does yield spiritual fruits but is considered partial and may not be sufficient for the ultimate spiritual goal. The highest and most certain service for attaining salvation is described as writing the biography of one's own Sadguru with pure devotion and then personally studying and reciting it regularly. This is considered the most effective path.