तस्माच्छास्त्रं प्रमाणं ते कार्याकार्यव्यवस्थितौ।ज्ञात्वा शास्त्रविधानोक्तं कर्म कर्तुमिहार्हसि॥
tasmāc chāstraṃ pramāṇaṃ te kāryākārya-vyavasthitaujñātvā śāstra-vidhānoktaṃ karma kartum ihārhasi
Word by word
The verse says
So let the scriptures be your measure for what is to be done and what is not. Knowing what they lay down, you should act, here, now.
In plain words
The chapter ends on an instruction, and the last word of it is iha - here.
Not later. Not once you have sorted yourself out. Here, in the situation you are actually standing in.
For Arjuna that means a field he does not want to be on. Twenty-three verses on what goes wrong inside a person, and the ending points outward at the day in front of him.
Where you've felt this · in parenting
Your daughter asks why she has to be home by nine when her friend does not. You find you cannot produce a reason that survives her follow-up question. You say it anyway, she goes along with it, and you spend the evening slightly bothered. Then you work out what you actually think, and you tell her the next day. The rule did not change. You had been running on something you had never examined, and now you are not.
Going deeper
Ending on here is the move that stops all of this from being an essay about bad people.
The last word points at the place the listener is standing. Arjuna is on a field he does not want to be on, facing a decision he has been avoiding since the first chapter. He has just heard a long account of how a person goes wrong, and what he is handed at the end of it is not a programme of self-improvement. It is: now act, here.
The measure offered is the tested teaching, and the reason is the one that has been building all along. Your own judgement is exactly the instrument that the three doors interfere with, so judgement cannot be the only check on itself.
What that leaves you with is modest and usable. Keep something outside your own appetite that you consult - a teaching, a practice, a person who will disagree with you. Not because you cannot be trusted. Because nobody can be, alone, and the ones who thought otherwise are the subject of this chapter.