What exactly was the 'Ishavasya-Bhavartha-Bodhini' that Das Ganu was writing, and why was he finding it so difficult?

The 'Ishavasya-Bhavartha-Bodhini' was a commentary on the Ishavasya Upanishad that Das Ganu had started. As described in Chapter 20, his intention was to make the profound meanings of this scripture accessible to people who were ignorant of the Sanskrit language by compiling an explanation in simple Prakrit (Marathi) Ovi verses. The difficulty arose because the Upanishad is "full of deep meanings." Though Das Ganu managed a word-for-word translation, he realized he had not understood the "internal secret" of the text. This lack of deeper comprehension meant his work felt hollow, and his mind "found no joy" in the project.