What does this chapter say about the role and importance of a Sadguru in a devotee's life?

According to Chapter 10, the Sadguru, or great Guru, is paramount in a devotee's spiritual journey. The text describes the Guru as the "one eternal God" who can alter a person's destiny, an act metaphorically described as striking "a nail over the lines of destiny." By placing trust in the Sadguru, a devotee can cross the "ocean of existence" (Bhavasagar), just as one trusts a boatman to cross a worldly ocean. The chapter states that when the Guru sees a devotee's faith, He grants them Knowledge (Samvitti) and liberation (Moksha) effortlessly. Furthermore, His grace can destroy worldly existence (Samsara) and untie the knot of birth and death, making devotion to the Guru the best and simplest spiritual practice.