Next, the freedom from action - naiskarmya, which is the result of karma-yoga attitude, is to be told.
asaktabuddhiḥ sarvatra jitātmā vigataspṛhaḥ । naiṣkarmyasiddhiṁ paramāṁ sannyāsenādhigacchati ॥18.49॥ The one whose mind is free from attachment everywhere, who has self-mastery, and from whom longing has gone, gains the most exalted accomplishment of action less by renunciation.
asaktabuddhiḥ - one whose mind has no attachment, who is a karma-yogī, he is not attached to likes and dislikes - rāga-dvesa. Our day to day activities are totally dedicated to fulfilling these rāga-dvesa. There is nothing wrong with this, but the problem comes only when there is an intense reaction if they are not fulfilled. What does it mean to be not attached to rāga-dvesa? It means my attitude towards the result of karma, either I like or I don’t like, more or less I keep the sameness of mind (samatvam yoga ucyate Gītā 2-48), neither exhilaration nor frustration. This is not a simple detachment, but it is possible only through understanding. The more we understand how karma-phala is futile, the easier to have the attitude of karma-yoga. This freedom from attachment extends to everything, therefore Lord Krsna says sarvatra - everywhere, extends to children, spouse, etc.
In other words, he is jitātmā - one who has mastery over his mind. He has gained this mastery through living a life of karma-yoga, keeping rāga-dvesa under check. He allows dharma and duty to rule his life but not rāga-dvesa, and thus, has mastered his mind. His mind is available for him to do whatever is necessarily to be done, and also he is free to do whatever he thinks can be done without pressure.
Then again, being one who has self-mastery, naturally he is the one who is released from longing for various things - vigataspṛhaḥ. Giving up things doesn’t always mean that the pressure to have those things is gone. Sometimes they are given up, but the value remains. We compromise and reconcile ourselves to the fact that we don’t need them. But the freedom from longing that we are talking about here doesn’t involve that kind of giving up. There is a cognitive appreciation of the limitations of all the various pursuits that can bring about certain dispassion - vairāgya which is an objective way of looking at things. When one can be objective, the longing is gone and one is a vigataspṛhaḥ.
asaktabuddhiḥ, jitātmā, and vigataspṛhaḥ are the results of karma-yoga which are the characteristics of freedom from action - naiskarmya in a certain measure. This freedom is fully gained only by clear vision of ātmā - sannyāsenādhigacchati. Sannyāsa here is not formal renunciation, but sarva-karma-sannyāsa - freedom from all karma as the result of self-knowledge. Gītā 5.13 - the indweller of the physical body, having renounced all actions mentally (by knowledge, knowing that oneself is non-doer), remains happily in the body (while living), neither performing any action, nor causing others to act.
Next verse explains briefly the method by which one fully gains freedom from action, characterised by jñāna-niṣṭhā.
siddhiṁ prāpto yathā brahma tathāpnoti nibodha me ।
samāsenaiva kaunteya niṣṭhā jñānasya yā parā ॥18-50॥ Learn from me in brief, Kaunteya (Arjuna)! How the one who has gained the accomplishment (of antaḥkaraṇa-śuddhi) gains the ultimate certainty of the knowledge that is Brahman.
Here the accomplishment - siddhiṁ is preparedness of mind. Śankarācarya explained it as the availability of our body-mind-senses when we need them. It is not just clarity of mind, but also body should be fit, both require grace.
What is that one who has gained this accomplishment - siddhiṁ prāptaḥ, going to accomplish later? He gains Brahman - brahma tathāpnoti in the form of certainty of knowledge of Brahman which is the ultimate end of knowledge niṣṭhā jñānasya yā parā. The culmination of this pursuit is its niṣṭhā - abidance in one’s own nature without obstruction, understanding that limitless Brahman is not another entity different from me, it is the self-evident me. What makes this knowledge so difficult to understand? Because the subject matter of this knowledge is about myself which is always evident to me. Śruti as pramānam tells me that I am not this body-mind-senses, but sat-cit-ānanda Brahman, but I don’t experience so. In this case this knowledge becomes only a paroksa-jñāna - indirect knowledge. It shouldn’t be considered as knowledge but śraddha in what śāstra says. If the listener has all the necessary qualifications, there is no obstruction to this knowledge. It becomes a clear immediate knowledge - aparoksa jñāna which I own up.