18:16 – One who has seen brahman meditates, “I am brahman.” What does one who has transcended all thought think, when they see no second?
“One who has seen brahman” is someone with indirect knowledge—they’ve been told about brahman by a teacher or text but they don’t yet understand that they are brahman. Meditating on their identity with brahman is therefore required until they can see for themselves that it’s true. Then they “see no second,” meaning they understand that everything in the universe is none other than their own self. This is self-knowledge, the vision of non-duality, which by definition transcends all thought, seeing as all thought, being based on words and concepts, is dualistic by nature.
18:17 – One who see distraction in themselves practices control. But the great one is not distracted. Having nothing to accomplish, what do they do?
When you believe that you’re the mind, you identify with its various states. For instance, if the mind is distracted, you think “I’m distracted.” In that case you may attempt to control and concentrate the mind through meditation. But when you become a “noble one” (one with self-knowledge), you see that the mind neither belongs to you nor affects you—as the self you’re never distracted. So as the self there’s nothing to be done because no amount of meditation can change your true nature. But that doesn’t mean meditation suddenly becomes useless for the mind. In that regard it’s always a helpful, healthy exercise that promotes focus and calm—even after enlightenment—should you choose to do it.
18:18 – The one with knowledge is no ordinary person, although they may live like one. They see neither concentration nor distraction nor defilement of their own self.
The one with knowledge is no ordinary person because they know that they’re not a person at all. But that doesn’t mean the body-mind they appear to be will act any differently than an ordinary person. For instance, if a banker realizes that they’re the self, they’ll most likely keep going to work, setting up accounts, giving out loans etc. They’ll still come home, eat dinner and spend time with their family. Outwardly, they appear totally ordinary. But inwardly, the way they think of themselves—as the self—is not like an ordinary person at all.
18:19 – The wise one who is beyond duality is satisfied and free from desire. They do nothing even when they appear to be acting in the eyes of the world.
The meaning of this verse is similar to the one above: the one with knowledge acts like a regular person. But the difference is that they know that they’re always the action-less self, despite the actions of the body-mind.
18:20 – The wise one who lives happily, doing what needs be done, does not feel eagerness either in activity or in inactivity.
When you’re a “wise one,” one with self-knowledge, your perspective on action changes. Knowing you’re not the doer—the body-mind—you can relax a bit and let the body-mind respond to what needs to be done, without excessive concern about what it does or doesn’t do.