According to the text, what is the prerequisite for truly understanding profound spiritual writings like the Upanishads?

The text emphasizes that intellectual prowess or scholarly knowledge alone is insufficient to grasp the deep meaning of spiritual texts like the Upanishads. Chapter 20 states that the essence of the Vedas and the treasure of the Upanishads are "very difficult to grasp" without the grace of God and a Guru. It warns that a scholar's attempt to comprehend them through self-effort will fail "even at the end of an era." The true prerequisites, as mentioned in chapter 20, are humility, detachment, and a strong attachment to the Guru's feet. For such a devoted individual, the hidden meanings open up automatically, and the path to Self-knowledge becomes clear.