What does the provided text say about the necessity of a Guru for understanding profound spiritual texts like the Upanishads?

The text in Chapter 20 strongly emphasizes that a Guru is indispensable for understanding profound spiritual knowledge. It states that the Upanishads contain the essence of the Vedas, a treasure that is 'very difficult to grasp' without the grace of God and Guru. The author warns that even a self-proclaimed scholar who tries to comprehend these texts through their own efforts will fail, as the 'hidden truth does not come to hand' without a Guru's grace. In contrast, for a devotee attached to the Guru's feet, there is 'not even a bit of difficulty,' and the concealed meanings open up automatically. This science of Self-knowledge is considered a weapon against the cycle of birth and death, accessible only to the humble and detached.