What is the most effective form of Guru service for attaining salvation, as described in the preface?

According to the preface in Chapter 0, the best and most certain form of service for achieving salvation is to write the biography of one's own Sadguru. This act should be undertaken either by the Guru's command or through inner inspiration. It is not enough to simply write it; one must also personally study it regularly, performing readings like Parayans and Saptahs with a firm resolve, pure heart, excellent faith, and unwavering devotion. This service, which engages the body and speech, does not interfere with family life. The text further clarifies that when this service is performed with a selfless (Nishkam) mind, aimed at liberation, it is considered far superior to service done with a desire (Kamya) for worldly gains.