Krishna says, "To you who doesn't cavil I shall reveal the sublime mystery -knowledge and wisdom. Once this is known, you shall be free from evil (9.1). The royal knowledge, the royal secret the supreme purifier is this, directly realisable, righteous, very easy to practice, imperishable (9.2).
Men devoid of 𝙎𝙝𝙧𝙖𝙙𝙙𝙝𝙖 in this 𝘿𝙝𝙖𝙧𝙢𝙖, without attaining Me, tread the death darkened path of 𝙨𝙖𝙣𝙨𝙖𝙧𝙖 (mortal world)" (9.3).
Krishna sets two conditions to be eligible to get this regal knowledge. The first is having 𝙨𝙝𝙧𝙖𝙙𝙙𝙝𝙖 (trust) and in the absence of 𝙨𝙝𝙧𝙖𝙙𝙙𝙝𝙖, even royal knowledge becomes a mere arrangement of words.
The second is being free of cavil, which essentially means avoiding finding faults. In a contemporary context, this phenomenon is described as 'we see the world as we are but not as it is'. When two people perceive the same thing or situation in two different ways, differences are bound to be there leading to the bitterness we see around. When cavilling is dropped divisions disappear and everything is actively accepted as a blessing of the almighty.
Incidentally, fulfillment of these two conditions is essential for one to be a 𝙗𝙝𝙖𝙠𝙩 or a devotee which is beyond performing the ritualistic practices imposed by the belief systems.
Krishna starts revealing this as Arjun showed himself to be ready for this knowledge like a 𝙗𝙝𝙖𝙠𝙩 and Krishna assures that once this is known one is free of the evils of 𝙨𝙖𝙣𝙨𝙖𝙧𝙖. Certainly, knowing can't be at the level of words, but at the level of being. Knowing at the level of words would invariably lead to the enhancement of 𝘼𝙝𝙖𝙣𝙠𝙖𝙖𝙧 as one feels that they know more than others. But when it is at the 'being' level one attains ultimate freedom or 𝙢𝙤𝙠𝙨𝙝𝙖. It is like being truthful in every moment of living along with knowing the truth.