Can you explain the philosophical concept of non-duality as described in Chapter 40?

Chapter 40 delves into the philosophical concept of non-duality, primarily through the relationship between the Guru and the devotee. The text explains that Shri Sai has the power to destroy the sense of duality, dissolving the separate feelings of 'me' and 'you.' This is further illustrated with the analogy of a river and an ocean; though they have different names, they are essentially one, and when they meet, no difference remains. According to Chapter 40, this union occurs when a devotee seeks exclusive refuge in the Sadguru with true devotion, at which point the Guru grants them His own Guru-nature, erasing the separation between them.