According to Chapter 20, why is relying on one's own scholarship insufficient for understanding the Upanishads, and what is the prescribed alternative?

Chapter 20 of the Sai Satcharitra argues that self-reliant scholarship is inadequate for comprehending the profound truths of the Upanishads because they represent the 'treasure of the four Vedas,' which is 'very difficult to grasp' without divine aid. The chapter explicitly states that a scholar who thinks, 'I am a scholar; by my own efforts I will comprehend the Upanishads,' will fail because 'without Guru's grace the hidden truth does not come to hand.' The prescribed alternative, as detailed in Chapter 20, is humility and devotion. For one who is 'attached to the Guru's feet,' there is 'not even a bit of difficulty,' as the hidden spiritual meanings will open up before their eyes automatically.