What philosophical argument does Chapter 20 make about the necessity of a Guru for understanding scriptures like the Upanishads?

Chapter 20 of the Sai Satcharitra makes a strong case that a Guru's grace is indispensable for comprehending profound scriptures. It explains that the Upanishads contain the very essence of the four Vedas, and grasping their meaning is exceedingly difficult without the grace of both God and a Guru. The chapter warns that even a great scholar who attempts to understand the Upanishads through their own efforts alone will fail, as the hidden truth is not revealed without Guru's grace. In contrast, for a devotee who is humble, detached, and attached to the Guru's feet, the path becomes easy, and the hidden meanings of the science of Self-knowledge open up automatically.