How does the author differentiate between general spiritual knowledge texts and a Guru's biography, and what common purpose can they both serve?

The author distinguishes between general spiritual knowledge texts and Guru biographies based on their content and focus. While the former are described as containing 'purely worldly and spiritual knowledge,' Chapter 0 defines a Guru's biography as a specific and reliable book detailing a Guru's incarnation, including their life stages, 'Leelas' (wonderful plays), and miracles. Despite this difference, both types of texts serve a dual purpose. They can be utilized with a 'Kamya' (desire-filled) intent for worldly prosperity or with a 'Nishkam' (selfless) intent for spiritual liberation from the cycle of birth and death.