Can you explain the specific Bhagavad Gita verse mentioned in Chapter 50 and the significance of the 'Avagraha'?

Chapter 50 discusses a verse from the fourth chapter of the Bhagavad Gita: "Tadviddhi pranipatena pariprasnena sevaya | upadeksyanti te jnanam jnaninastattvadarsinah ||". The author points out a subtle detail in the third line, where an Avagraha (a grammatical symbol) can be perceived before the word 'Jnana' (knowledge). This Avagraha is interpreted as an indicator of 'Ajnana' (ignorance). The implication is that the verse is instructing one to first understand ignorance. The text clarifies that without considering this Avagraha, the word is simply 'Jnana', which aligns with the universally accepted Vedic principle that knowledge alone leads to liberation.