What is the philosophical teaching in Chapter 20 regarding the role of a Guru in understanding profound spiritual texts like the Upanishads?

Chapter 20 emphasizes the indispensable role of a Guru for spiritual understanding. It states that the Upanishads, which contain the essence of the Vedas, are very difficult to grasp without the grace of Hari (God) and the Guru. The text explicitly warns that a scholar's attempt to comprehend these texts through their own efforts alone is futile, stating the hidden truth will not come to hand as the path is difficult at every step. In contrast, for a humble and detached devotee who is attached to the Guru's feet, the hidden meaning opens up automatically without any difficulty. This highlights the concept that self-knowledge is only accessible through humility and a Guru's grace.