What does the preface say is the most effective form of written service to a Guru for attaining salvation?

According to the preface, the best and most certain written service for attaining the fruit of salvation is to write the biography of one's Sadguru. As detailed in Chapter 0, this should be done either by the Guru's command or through inner inspiration. This service is not just about writing; it also involves personally studying the work regularly, performing hundreds of readings called Parayans, and conducting weekly recitations known as Saptahs. This must be done with a pure heart, selfless love, and unwavering devotion to be truly effective. This practice is also compatible with maintaining family responsibilities.