Arjuna opens the third chapter with a fair complaint. If understanding really is better than action, why is he being pushed into a terrible one? He suspects, reasonably, that he is being given mixed counsel and asks for a single answer.
The reply begins with an observation rather than a doctrine. No one remains without acting even for an instant, because everyone is made to act by the strands of their own nature whether they consent or not. Breathing, digesting, thinking and wanting all continue. Someone who restrains the organs of action while the mind still runs over their objects is not a renouncer but a hypocrite, and is in a worse position than the person who simply does the work with the senses governed.
That is the argument that closes off Arjuna's escape route, and it is worth noting how modest it is. It does not claim that action is holy. It claims that inaction is not available, so the only real question is the manner of acting. The chapter then supplies the manner: work offered as sacrifice, in a world imagined as a system of mutual giving in which rain, food, creatures and offering each sustain the next. Someone who takes from that cycle without contributing is described bluntly as a thief.
The chapter ends by naming what actually stops people. Arjuna asks what drives a person to wrong action as if by force, and is told it is desire, which turns to anger when thwarted, and which is seated in the senses, the mind and the understanding, from where it clouds knowledge as smoke clouds fire.