What kind of texts are considered most suitable for performing a Parayan or Saptah, and why are some works less ideal for this purpose?

The preface in Chapter 0 clarifies that for a Parayan or Saptah focused on a single saint, the most suitable texts are detailed, poetic, comprehensive, and famous works. While one can perform a Parayan of collections like Shri Bhaktalilamrut, they are not ideal for this specific purpose because the biographies within them are often not comprehensive, sometimes spanning only two or three pages. To truly facilitate deep study and devotion, a more substantial and singular biography is needed. The text points to the Brihat Guru Charitra and Shri Sai Satcharita as prime examples of works that are perfectly suited for Parayans and Saptahs due to their detailed and graceful nature.