What is the 'science of Self-knowledge' as described in Chapter 20, and who is considered worthy of it?

In Chapter 20, the profound wisdom contained within the Upanishads is referred to as the 'science of Self-knowledge.' This knowledge is portrayed as a powerful weapon that can cut through the cycle of birth and death. The chapter makes it clear that this is not merely academic learning but a deep, hidden truth that cannot be grasped by intellectual effort alone. According to the teachings in Chapter 20, accessing this knowledge is extremely difficult without the grace of a Guru. Furthermore, the text specifies that only those who are 'humble and detached' are considered worthy of discussing and receiving this profound science of Self-knowledge.