Can you provide a summary of the key themes and narratives presented in Chapter 20 of the Sai Satcharitra?

Chapter 20 of the Sai Satcharitra begins by praising Sai as a 'Siddhashram' (abode of the perfected) whose presence removes worldly fatigue. It then vividly describes the scene in Shirdi after the noon Aarti, where Sai Baba lovingly distributes Udi to his devotees, applying it to their foreheads with his thumb. The chapter transitions to introduce the story of Das Ganu, who was attempting to write a commentary on the Ishavasya Upanishad. As Chapter 20 explains, Das Ganu encountered a doubt he could not resolve and went to Baba, who mysteriously told him the answer would be revealed by a maidservant. The chapter also philosophically discusses the immense difficulty of understanding scriptures like the Upanishads without the grace of a Guru.