What was Das Ganu's project, and what specific challenge did he face, as detailed in Chapter 20?

According to Chapter 20, the devotee Das Ganu had undertaken a project to create a commentary on the Ishavasya Upanishad, titled "Ishavasya-Bhavartha-Bodhini." His goal was to explain the meaning of this profound scripture in simple Prakrit language for those who were not learned in Sanskrit. However, he encountered a significant challenge. Although he translated the text word for word, he found that he could not grasp the internal secret or deeper meaning, and his mind found no joy in the work. This led to a specific doubt which he took to his Satguru, Sai Baba, in Shirdi.