What are the different types of biographical writing the author discusses, and which one does he consider the most spiritually beneficial?

The author outlines a hierarchy of biographical writing as a form of service. As detailed in Chapter 0, writing about worldly figures is a service, but its fruits are temporary and not purely spiritual. A higher form is writing about many saints, which yields spiritual benefits but is still considered partial. The author asserts that the most certain and beneficial service for attaining salvation is writing the biography of one's own Sadguru. This act, especially when undertaken with a pure heart, unwavering devotion, and selfless love, is presented as the supreme form of literary Guru service that can lead to the ultimate spiritual goal.