सिद्धिं प्राप्तो यथा ब्रह्म तथाप्नोति निबोध मे।समासेनैव कौन्तेय निष्ठा ज्ञानस्य या परा॥
siddhiṃ prāpto yathā brahma tathāpnoti nibodha mesamāsenaiva kaunteya niṣṭhā jñānasya yā parā
Word by word
The verse says
Learn from me, briefly, how someone who has reached that fulfilment also reaches the absolute, which is the highest ground that knowing can stand on.
In plain words
A hinge verse, announcing the final stretch.
And the word samāsena - briefly - is a kindness. He knows how long this has been.
What follows is the last description of the path, compressed into four verses. After that the book stops teaching and starts speaking to Arjuna directly.
Where you've felt this · in study
At the end of a long course the teacher takes twenty minutes to say the whole thing again from the top. Nobody objects. The second pass is the one where people see how the pieces sit together, and several of them understand something in those twenty minutes that eleven weeks had not delivered.
Going deeper
Summarising at the end, after everything has already been said, does something that the original explanation cannot.
The first pass through difficult material has to build each piece before it can be used, so you meet the parts in an order dictated by what depends on what. The shape of the whole is not visible while that is happening.
A summary given afterwards is a different object. Every term in it is already understood, so for the first time the listener can see the proportions: what was the main line and what was an aside.
It also carries a quiet signal that matters for a reader. If the whole thing can be said briefly at the end, then the length was not the point. The length was the route, and routes are longer than the places they go.