The text describes a hierarchy of biographical writing as a form of service. Can you detail this hierarchy, from least to most spiritually potent, and explain the ultimate method prescribed for attaining salvation?

The text in Chapter 0 presents a clear hierarchy regarding the spiritual efficacy of writing biographies. At the lowest level is writing about worldly figures, which is a service limited by time and space and yields no spiritual fruit. A step above this is writing the biographies of many different saints; this is a valid form of Guru service that yields spiritual fruit but is described as 'one-sided or partial' and possibly insufficient for attaining the ultimate goal. The supreme and 'most certain service' that grants salvation is to write the biography of one's own Sadguru, undertaken with a pure heart, unwavering devotion, and selfless love. This act, combined with regular personal study and recitation (Parayans), is presented as the most direct path to the ultimate spiritual goal.