What is the relationship between Guru's grace and understanding the 'science of Self-knowledge' as described in the text?

The provided text from Chapter 20 emphasizes that Guru's grace is indispensable for understanding the 'science of Self-knowledge,' which is described as a weapon that can cut through the cycle of birth and death. The source states that without the grace of Hari (God) and Guru, grasping the essence of scriptures like the Upanishads is very difficult. Attempting to comprehend this hidden truth through one's own scholarly efforts is futile. However, for those who are humble, detached, and attached to the Guru's feet, there is no difficulty. The hidden meaning reveals itself automatically, and clarity is achieved. Das Ganu's own experience with the Ishavasya Upanishad is presented as an example: once Sainath showed his grace, the difficulty he was facing vanished.