The text mentions a verse from the Bhagavad Gita. What is the verse and what is its special significance regarding 'Ajnana'?

Chapter 50 references a verse from the fourth chapter of the Bhagavad Gita: "Tadviddhi pranipatena pariprasnena sevaya | upadeksyanti te jnanam jnaninastattvadarsinah ||". The significance highlighted in this chapter is a subtle linguistic interpretation. It points out that in the third line of the original verse, an 'Avagraha' (a grammatical symbol) can be found before the word 'Jnana' (knowledge). The text proposes that this Avagraha serves as an indicator of 'Ajnana' (ignorance). This interpretation is used to initiate a deeper discourse on the nature of ignorance and how it must be understood and removed before true knowledge can be imparted by the knowers of truth.