What challenge did Das Ganu face while writing his commentary on the Ishavasya Upanishad, and what was Sai Baba's enigmatic instruction to him in Chapter 20?

According to Chapter 20, Das Ganu was composing a Marathi commentary called the 'Ishavasya-Bhavartha-Bodhini' to make the Upanishad accessible. Although he translated it word for word, he couldn't grasp its deep, internal secret, and his mind found no joy in the work. Plagued by a significant doubt, he went to Shirdi to seek guidance from his Satguru. Instead of providing a direct explanation, Sai Baba gave him a mysterious instruction. Baba told him, 'The resolution of this doubt of yours will be done by the maidservant at Kaka’s house when you return there,' setting the stage for a profound, indirect teaching.