From a philosophical standpoint, why is writing a biography of one's Sadguru considered a complete spiritual service, while other biographical works are deemed partial or worldly?

Philosophically, writing about one's Sadguru is presented as a complete spiritual service because it is an act of selfless love and unwavering devotion directed toward the ultimate spiritual guide. Chapter 0 explains that this service, when coupled with personal study, leads to salvation. In contrast, writing about worldly figures is considered a worldly service that is limited and often tainted by self-interest, thus yielding no spiritual fruit. Even writing about many saints, while a valid form of Guru service, is called partial because it lacks the focused, personal devotion to the one Sadguru who is the direct means to the ultimate spiritual goal. The service to one's Sadguru is uniquely positioned to grant salvation without interfering with worldly duties.