Krishna adds a crucial condition. Yes, yajna, charity, and austerity must be performed — but without attachment, and without craving for results. Perform the action. Release the outcome. This, Krishna says, is my definitive and highest view.
The word 'uttamam' stands out. Krishna does not say 'this is one way to look at it.' He says: this is my supreme opinion. In a text where Krishna often presents multiple paths with equal grace, this kind of emphasis is rare. He wants no confusion on this point.
This is the essence of nishkama karma — selfless action — restated in the final chapter with full force. Do good work. Offer it freely. Do not keep a mental ledger of what you are owed in return.