18:36 – An ignorant person does not attain liberation through repeatedly practicing control of the mind. The blessed one through mere knowledge becomes free and unaffected by change.
You’re the self so no amount of controlling the mind can turn you in to the self you already are. That’s why liberation is a matter of knowledge—meaning understanding what’s already true—not a matter of action.
18:37 – The ignorant person does not attain brahman because they desire to attain it. The wise one certainly realizes the nature of the brahman, even without desiring to do so.
If a person desires to attain brahman, they’re thinking of brahman as something outside of and separate from themselves that they need to acquire, merge with, or become. But this thinking is incorrect (ignorant) because brahman isn’t outside of anyone or separate from anything—this means, ironically, that the one who desires to attain brahman already is brahman.
That’s why the wise one realizes the nature of brahman when they stop desiring it, meaning when they stop viewing brahman as something other than their own self.
18:38 – Without the support of knowledge, the ignorant seek fulfillment in the world. The wise cut the very root of this world which is the source of all misery.
“The very root of this world” is ignorance, specifically ignorance of the fact that the world—while seemingly real—is actually an illusory appearance of the self, consciousness-existence. So instead of seeking fulfillment in the world, the wise destroy its root cause with self-knowledge, thereby negating the misery caused by trying to find satisfaction in something that isn’t real.
18:39 – The fool desires peace through control of the mind and so does not attain it. The wise one knows the truth and is ever of tranquil mind.
Control of the mind is an action. Since action only produces limited, temporary results, no lasting peace is possible. The wise, therefore, seek knowledge. When they know the truth, “I am brahman,” their minds can rest easy in the knowledge that as consciousness-existence they’re limitless, eternal, unchanging and ever-free no matter what condition the mind is in.
18:40 – Where is self-knowledge for him whose knowledge depends on the object? The wise do not see objects—they only see the immutable self.
The self, despite being the substratum of all objects (an object being any aspect of the body-mind or world), is never itself an object. So any knowledge based on knowing objects can’t be self-knowledge.
The wise are the wise because they have non-dual vision—even though they see objects like anyone else, they know that the objects are only an unreal appearance of their own self.