स्थितप्रज्ञस्य का भाषा समाधिस्थस्य केशव।स्थितधीः किं प्रभाषेत किमासीत व्रजेत किम्॥
sthita-prajñasya kā bhāṣā samādhi-sthasya keśavasthita-dhīḥ kiṃ prabhāṣeta kim āsīta vrajeta kim
Word by word
The verse says
Arjuna said: How would you describe someone whose understanding has settled, Krishna, someone steady in that state? How does a person like that speak? How do they sit? How do they walk?
In plain words
Arjuna asks the best question in the chapter, and it is completely practical.
Not what is the nature of the settled mind. How do they sit? How do they walk?
He wants to know what one looks like coming down the street.
Where you've felt this · at work
Somebody describes a good manager in the abstract and it is all fine and useless. Then they say: she always reads the thing before the meeting. Now you know what to do on Monday.
Going deeper
This question changes the whole book, and it comes from the student rather than the teacher.
Krishna has been speaking about the deathless self, the bondage of action, the settled mind. Arjuna, who is a soldier and not a philosopher, asks for a description he could recognise on sight.
It is not a lesser question. It is the question that keeps the Gita from becoming abstract, and Krishna takes it seriously enough to spend the entire rest of the chapter — eighteen verses — answering it.
Sthita-prajña — one whose knowing has come to rest. The term is introduced here and becomes one of the book's key ideas. Chapter 12 and Chapter 14 will give their own versions of this portrait.
Notice the progression in Arjuna's three questions: speech, sitting, walking. From the most deliberate to the least. How you talk can be managed for a while. How you walk cannot.
He is asking, in effect: what does this look like when nobody is trying?