According to the preface, what is considered the most effective and certain form of Guru service through writing, and how should it be practiced?

The preface describes the best and most certain service as writing the biography of one's own Sadguru, either by their command or through inner inspiration. This practice is not just about writing; it involves personally studying the biography regularly, performing hundreds of readings (Parayans), and conducting weekly recitations (Saptahs). As detailed in Chapter 0, this should be done with a firm resolve, pure heart, excellent faith, selfless love, and unwavering devotion. This form of service, which engages both body and speech, is considered spiritually superior and does not interfere with maintaining one's family life.