If a jñānī - wise person seeing himself/herself is the non-doer ātma, will he/she still perform action?
yasya sarve samārambhāḥ kāmasaṅkalpavarjitāḥ |
jñānāgnidagdhakarmāṇaṃ tamāhuḥ paṇḍitaṃ budhāḥ ||4-19||
The one for whom all undertakings are free from binding desire and will, whose actions are burnt by the fire of knowledge, the sages call him as wise.
When a jñānī undertakes any activity, he/she does so without kāma - desire and sankalpa - will. He/she performs action neither without selfish desire nor for one's own satisfaction. All actions of a jñānī are only for exhausting of prārabdha-karma. The prārabdha-karma of a person has to run its course. Jñānī's actions will not produce punya or pāpa because he/she knows him/her self is not the doer. He/she is seeing oneself as non-doer in every action. When one is not the doer, he/she will not be the enjoyer of the result. Therefore results of actions are burned by the knowledge of the self "I am non-doer ātmā", just like roasted seeds which can't be germinate further.
How is the mindset of a wise person while doing action?
tyaktvā karmaphalāsaṅgaṃ nityatṛpto nirāśrayaḥ |
karmaṇyabhipravṛtto'pi naiva kiñcitkaroti saḥ ||4.20||
Giving up the deep attachment to the results of action, always contented, being not dependent on anything, he/she does not do anything even though fully engaged in action.
Nobody do action for the sake of action, we all act for the sake of enjoying the result. Attachment toward result is the source of our happiness and sorrow. For jñānī who knows the result of action will not come to him/her since he/she is not the doer of the action, therefore there is no attachment toward result of action. A jñānī's welfare doesn't get better or worse, his/her happiness doesn't increase or decrease, no matter what action he/she does. As a non-doer, one has given up all dependence and attachment as an experiencer of the result - tyaktvā karmaphalāsaṅgaṃ.
Nirāśrayaḥ - free from all dependence. A jñānī doesn't depend upon the the accomplishment of purusārtha (goals of life) to be alright like the ignorance person does.
Because by knowing I am ātmā is satyam (independent reality), and all other anātmā is mithya (experiential reality which dependent on satyam to be exist), a jñānī is nirāśrayaḥ. I am being alright doesn't depend upon any accomplishment. On the other hand, success or failure is depended on my attitude and mind set while facing the condition.
Nityatṛptah - he/she is contented with what is unfolded by prārabdha. Because by knowing "I am pūrnah - whole", one's feeling of containment cannot be added on nor subtracted by any result of actions. This verse is describing a grhastha-jñānī (one who liberate even still active in social life), even fully engaged with activities, but he/she is not bound by karma.
Next, the lifestyle of a sannyasī jñānī is being talked about.
nirāśīryatacittātmā tyaktasarvaparigrahaḥ |
śārīraṃ kevalaṃ karma kurvannāpnoti kilbiṣam ||4.21||
The person who is free of expectations, whose body, mind and senses have been mastered, who has given up all possessions, doing only action that sustains the body, does not incur sin.
nirāśīh - a jñānī is free from expectation. It is different from a karma-yogī who accepts the result of actions as prasāda. A karma-yogī is not under the spell of likes and dislikes, but the doership is still there with regards of karma. Action is to be done to fulfil his/her desire which is still there. On the other hand, a jñānī is totally free from desire because he/she has owned up the wholeness - pūrnatvam. When karma is to be done to fulfil one's desire, then is there any purpose for one who has complete fulfilment to perform karma? Therefore the jñānī described here is a sannyasī jñānī who has given up all karma and all possessions - tyaktasarvaparigrahaḥ.
This freedom is in part due to prior accomplishment in terms of mastery over the body-mind-sense-complex - yatacittātmā. Because when one still needs too much maintenance of the physical body, desires might raise for that needs. Hence he/she is the master of body, mind and senses, not the other way around. Therefore there are minimum karma for a sannyasī jñānī just for sustenance of the body in order to finish up his/her prārabdha-karma (whatever need to be done and experienced by this physical body in this birth). Therefore his/her karma doesn't give adverse result.
Why is it said to be adverse result? A jñānī's action does not give any favourable or unfavourable result. The word adverse is used because for one who wishes to release from this circle of samsāra, both punya and pāpa are considered to be adversity only, because they will bring about a new body to experience them.