According to Chapter 20, what is the most important requirement for truly understanding profound scriptures like the Upanishads?

Chapter 20 offers a profound teaching on the nature of scriptural understanding. The chapter asserts that intellectual prowess or scholarship alone is insufficient. It explicitly states that a scholar trying to comprehend the Upanishads through their own efforts will fail, as the path is 'difficult at every step' without a Guru's grace. The essential prerequisite, as explained in this chapter, is the grace of Hari (God) and the Guru. For a devotee who is humble, detached, and firmly attached to the Guru's feet, the hidden, esoteric meaning of the scriptures opens up automatically and without difficulty, unlike for the scholar who relies solely on their own intellect.