What does the phrase 'strikes a nail over the lines of destiny' mean in the context of Chapter 10, and what is required from the devotee?

The phrase "strikes a nail over the lines of destiny," found in Chapter 10, is a powerful metaphor for the Guru's ability to completely change a devotee's fate. The chapter explains that this extraordinary intervention occurs when a devotee places pure faith and devotion at the Guru's feet. The text posits that the Guru alone is the "one eternal God." Therefore, by surrendering to the Sadguru and engaging in His service, a devotee can have their destiny fundamentally altered, overcoming the predetermined course of their life. The key requirement from the devotee is unwavering faith in the Guru's power.