What is the core message of Chapter 20 regarding the necessity of a Guru for spiritual understanding?

Chapter 20 powerfully argues that a Guru's grace is essential for grasping deep spiritual truths. Using the context of Das Ganu's struggle with the Ishavasya Upanishad, the chapter states that while this scripture is the 'treasure of the Upanishads,' it is 'very difficult to grasp' without the grace of Hari and Guru. It dismisses the idea that a scholar can comprehend such texts through their own efforts, asserting that the 'hidden truth does not come to hand' without a Guru's help. Conversely, Chapter 20 assures that for one who is 'attached to the Guru's feet,' there is no difficulty, and the hidden meaning reveals itself automatically.