According to the preface, what are the different types of service through writing, and which one is considered the most beneficial for achieving the ultimate spiritual goal?

The preface outlines three main types of service through writing. The first, writing biographies of worldly Gurus, is described in Chapter 0 as being of a worldly nature, limited by time and space, and not yielding spiritual fruits. The second, writing biographies of many saints, is a form of Guru service that does yield spiritual fruits but is considered partial. The third and most highly recommended service is writing the biography of one's own Sadguru. As explained in Chapter 0, this service, especially when combined with regular study, Parayans, and Saptahs, is considered the best and most certain path to salvation.