Sankhya Yoga 2.21

 Verse 2.21

वेदाविनाशिनं नित्यं य एनमजमव्ययम् |

कथं स पुरुष: पार्थ कं घातयति हन्ति कम् || 21||

vedāvināśhinaṁ nityaṁ ya enam ajam avyayam

kathaṁ sa puruṣhaḥ pārtha kaṁ ghātayati hanti kam

veda—knows; avināśhinam—imperishable; nityam—eternal; yaḥ—who; enam—this; ajam—unborn; avyayam—immutable; katham—how; saḥ—that; puruṣhaḥ—person; pārtha—Partha; kam—whom; ghātayati—causes to be killed; hanti—kills; kam—whom

O Partha, how can one who knows the atma to be imperishable, eternal, unborn, and immutable kill anyone or cause anyone to kill?

Atma akarta (atma does not perform any action)

In this verse, Krishna shortly describes what he explained in the previous slokas about the nature of atma. Since atma does not undergo the six kinds of changes he calls it as avinashi (indestructible), ajam that has no birth, avyayam (that which is not subject to waning). The one who has this knowledge really knows the atma. He is the atma jnani (knower of the self). He has no ego (ahankara), hence he does not have any identification with his actions. He does not think, “I have done this.” or “I was instrumental for this action.” Since the teaching takes place in the battlefield, Krishna has taken the action of killing as an example. Arjuna is grieving about the death of his relatives and teachers. But Krishna says the one who knows atma to be himself and with the above said qualities does not kill anyone nor does he instigate someone to kill. 

There are two kinds of karta (agent of action). One is karta. The one who performs an action. The other is karayita or hetu karta. The one who makes someone else perform the action. An atma jnani is neither a karta nor a karayita.

Sarva karma sanyasi ( the sanyasi who renounced ownership of his actions).

A Sarva karma sanyasi does not have kartritva buddi (the sense of doership). With his mind as the backdrop, his senses perform various functions. But he remains in his true state with the realization that he is not the doer of any action. The one who has this knowledge is called vidvan. His prayers, his yoga, his spiritual practices to attain noble qualities all culminate in attaining this sarva karma sanyasa state. Shankara in his commentary says that he who has attained this state does not perform any action with the expectation of any desired result. By stating that all his prior karmas and upasanas were performed only to attain this state, he connects the karma shastra to vedanta shastra. Sarva karma sanyasa is the only real sanyasa.

Hence one can choose to live in family life (grihasta) and continue his life as a sarva karma sanyasi to spend his prarabdha. He does not have to physically renounce his materialistic possession to embrace a life of sanyasa as stated by the shastras. As long as one is a sarva karma sanyasi, meaning he renounced the doership of all his actions, then the ashrama he lives in does not really matter. People like king Janaka lived in worldly life and yet remained atma jnanis performing their actions as directed by their prarabdha. He does not do any action desiring a particular result. All his actions are directed by his own prarabdha. This view is strongly given in the Gita in various places.