What is Dharma in the Bhagavad Gita?
Dharma is usually translated as duty or righteousness, and both are a little misleading. The root means to hold or to bear, so dharma is closer to what holds something in its proper shape. The dharma of fire is to burn. The dharma of a person is harder, because it is not one thing.
The Gita uses the word in two sizes. There is dharma in general, the order that keeps a society and a life from falling apart. And there is sva-dharma, your own dharma: the particular work that follows from who you actually are, as against an imitation of somebody else's life.
What makes the Gita's treatment unusual is that it does not pretend this is simple. Arjuna's collapse in chapter 1 is not laziness. It is two real duties pointing in opposite directions, and the book never says that one of them stopped being real. 18.66, the last thing Krishna teaches, tells him to let go of all dharmas and take shelter instead, which only makes sense if the competing claims were genuine all along.
The verses 10
2.31
And if you look at your own work in the world, you have no reason to waver.
2.32
Lucky are the warriors who get a fight like this one, Arjuna - arriving unasked, an open door.
2.33
But if you will not fight this rightful fight, then you throw away your own work and your good name, and you take on the fault instead.
2.40
On this path nothing you begin is wasted, and nothing goes backwards.
3.35
Better your own work, done badly, than someone else's work done well.
4.7
Whenever what is right grows weak, Bharata, and what is wrong rises up, then I send myself forth.
4.8
To protect those who are good, to undo those doing harm, to set right what is right - I come into being, age after age.
18.31
The understanding by which you get right and wrong, and what should and should not be done, the wrong way round: that one, Arjuna, is driven.
18.47
Better your own work done imperfectly than someone else's work done well.
18.66
Let go of all duties and come to me alone for shelter.