Based on Chapter 20, what is the indispensable role of a Guru in comprehending the esoteric wisdom of the Upanishads?

Chapter 20 powerfully argues that understanding the deep truths of the Upanishads, described as the essence of the Vedas, is impossible without a Guru's grace. The text explicitly states that a scholar who arrogantly believes they can comprehend these scriptures by their own efforts will fail, as the hidden truth will not come to hand. This path is described as 'difficult at every step' without a Guru. Conversely, the chapter explains that for a humble and detached person devoted to the Guru's feet, there is no difficulty. For such a devotee, the hidden meaning of the science of Self-knowledge opens up automatically, providing the 'weapon that cuts through birth and death.'