Here Krishna lays down the philosophical core of Karma Yoga. All actions, without exception, are actually performed by the three gunas of prakriti — sattva, rajas, and tamas. The soul itself is a witness, untouched by any of it. But the person trapped in ego does not see this. They believe: I did it. I earned it. I deserve the credit.
This 'ahankaravimudhatma' — the one deluded by ego — is the root of all bondage. As long as the sense of 'I am the doer' persists, every action creates a chain. The moment that identification loosens, the action flows freely without binding the actor.