What is considered the most effective and certain form of written Guru service for achieving salvation, according to the Preface?

According to the preface from Chapter 0, while writing biographies of many saints is a form of Guru service, it is considered partial. The best and most certain written service that grants the fruit of salvation is to write the biography of one's own Sadguru. This act should be undertaken either by the Guru's direct command or through genuine inner inspiration. The service extends beyond just writing; it includes personally studying the work regularly, performing hundreds of readings (Parayans) and weekly recitations (Saptahs) with a pure heart and unwavering devotion, and encouraging others to do the same.