Chapter 50 mentions a specific verse from the Bhagavad Gita and something called an 'Avagraha'. What is the significance of this?

Chapter 50 discusses a verse from the fourth chapter of the Bhagavad Gita: "Tadviddhi pranipatena pariprasnena sevaya | upadeksyanti te jnanam jnaninastattvadarsinah ||". The text points out a subtle linguistic and philosophical detail concerning its third line. It suggests that an 'Avagraha' (a symbol in Devanagari script) emerging before the word 'Jnana' (knowledge) can be interpreted as an indicator of 'Ajnana' (ignorance). This interpretation is used to frame a discourse oriented toward ignorance. While the standard meaning of the verse is that knowers of truth will instruct you in knowledge, this subtle point raised in Chapter 50 highlights how even sacred texts can be analyzed to understand the nature of ignorance.