According to the preface, what is considered the most effective form of written service to a Guru for achieving salvation?

The preface clearly states that the best and most certain form of written service for attaining salvation is to write the biography of one's Sadguru. As detailed in Chapter 0, this act should be undertaken either by the Guru's direct command or through one's own inner inspiration. For this service to yield the ultimate spiritual fruit, it must be accompanied by regular personal study, including Parayans (hundreds of readings) and Saptahs (weekly recitations), all performed with a pure heart, unwavering devotion, and selfless love. This form of service is considered superior to writing about worldly figures or even multiple saints.