Krishna says that there is no kartha for any karma. Karma is in fact the result of the interaction among the three Gunas viz. Satva , Rajo and Tama which are a part of Prakriti (nature).
Krishna advises Arjun to transcend these Gunas to be free from sorrows. Arjun wanted to know how to be Guna-ateeth (transcending Gunas) and what a person would be like when he attains this state.
We have already discussed Dwandwa-ateeth (transcending polarities), Drishta (witness) and Samatva (equanimity), qualities that are enshrined in the Gita. Krishna indicates that a combination of these three constitutes Guna-ateeth .
According to Krishna, a person who has attained the state of Guna-ateeth is one who realizes that gunas are interacting with gunas and therefore, remains a saakshi (witness). He neither craves for a particular Guna nor is he averse to any other one.
Guna-ateeth is simultaneously Dwandwa-ateeth also. After understanding the polarities of pleasure and pain, he remains neutral to both. He is neutral to praise and criticism as he realises that these are products of the three gunas . Similarly, he is neutral to friends and enemies realising that we are friends to ourselves and also enemies to ourselves.
The physical world is polar and swings are natural. On the other hand a swinging pendulum also needs a stationary point. Lord Krishna is hinting at reaching that stationary point from where we can just witness the swinging without being part of it i.e. polarities.
Guna-ateeth gives equal importance to gold, stone and a handful of soil. This metaphorical comparison conveys that he doesn't assign higher value to one and lower value to another. He values things as they are, not as valued by peers.
Krishna further says that Guna-ateeth is one who shuns the feeling of Kartha . This happens when we realise, through our experiences that things are automatic and there is hardly place for Kartha .
Source - Daily World