Now Sri Krishna will talk about how one can stay detached further 

Bg 5.13

sarva-karmāṇi manasā

sannyasyāste sukhaṁ vaśī

nava-dvāre pure dehī

naiva kurvan na kārayan

Word for word: 

sarva — all; karmāṇi — activities; manasā — by the mind; sannyasya — giving up; āste — remains; sukham — in happiness; vaśī — one who is controlled; nava–dvāre — in the place where there are nine gates; pure — in the city; dehī — the embodied soul; na — never; eva — certainly; kurvan — doing anything; na — not; kārayan — causing to be done.

Translation: 

When the embodied living being controls his nature and mentally renounces all actions, he resides happily in the city of nine gates [the material body], neither working nor causing work to be done.

 

So Sri Krishna says, sarva-karmāṇi manasā -> All the work from mind what we do ? sannyasyāste -> So here Sri Krishna is talking about Manas sanyas, we have manas puja -> This means if a devotee cannot worship Sri Krishna directly, he can worship Sri Krishna in mind. So if we cannot offer Sri Krishna beautiful blue jewel necklace because we don’t have finance for this, we can do this offering in mind and pray Sri Krishna to accept it. So that is accepted as Sri Krishna sees our intention to serve Him to Glorify Him and He accepts our intention, this is at devotees level i.e. at Karma Yogi level manasā sannyasyāste, OK I am not the doer sarva-karmāṇi manasā

sannyasyāste, when I understand that I am not the doer, body has certain needs and those needs have to be fulfilled, so whatever needs are required for the body I will fulfill those needs sukhaṁ vaśī, such a person is able to stay happily sukhaṁ vaśī, how happy? Because there will be no messing up with troublesome sense objects, specially in terms of emotional entanglement with them, we will function in material world but we will not be emotionally entangled and nava-dvāre pure dehī, nava dvar refers to nine doors pure dehi, pura is the city, dehi is the soul who lives in the city of nine gates, naiva kurvan na kārayan such a person will not be the doer and will not be motivators for doing to others, In 3.1 ch Arjuna is asking Krishna why are you telling me to do such a ghastly thing

arjuna uvāca

jyāyasī cet karmaṇas te

matā buddhir janārdana

tat kiṁ karmaṇi ghore māṁ

niyojayasi keśava

Sri Krishna is saying that when you understand this philosophy completely then you will understand that neither you are doer nor I am making you to do anything, you will understand that it is material nature which is acting. To the extent we think that we are going to enjoy the senses we think that I am doing things and the extent we think that I am doing things the extent we will get entangled i.e. become bound in the material system, but to the extent we don’t think that we will not become bound. So what is this nava-dvāre pure dehī, nava dvara are the nine holes in the body 

 

Srila Prabhupad’s Purport: Śvetāśvatara Upaniṣad 3.18

nava-dvāre pure dehī

haṁso lelāyate bahiḥ

vaśī sarvasya lokasya

sthāvarasya carasya ca

“The Supreme Personality of Godhead, who is living within the body of a living entity, is the controller of all living entities all over the universe. The body consists of nine gates [two eyes, two nostrils, two ears, one mouth, the anus and the genitals]. The living entity in his conditioned stage identifies himself with the body, but when he identifies himself with the Lord within himself, he becomes just as free as the Lord, even while in the body.” 

The c part is repeated in Hitoupanish in3.18 a.

So what is described here is, Lord is situated in this body vaśī sarvasya lokasya, sthāvarasya carasya ca. When the living entity Vasi sarvasya lokasya situated in the conditioned stage identifies himself as this body, what are the nine gates of the body? Nine gates are [two eyes, two nostrils, two ears, one mouth, the anus and the genitals]. Just as in the city there are different gates, the entry points and exists points are those we interact to the world, we find good looking senses we wanted to enjoy so by Jayan Indriya we perceive some sensory impression comes inside and we engage in Indriya Trupti, certain sensory actions go out and we become bound, so interaction of soul with external world happens through gates just as every well protected city will not allow anyone and everyone to come inside not it will allow anything or everything to go outside e.g. if in a country foreign currency situation is delicate and country will not allow too much money to go out of it like that there is a regulation similarly, when one understands this body is like a city and one needs to regulate what is going inside and what is coming out of the body, then we can stay free from bondage, we understand that this body is like a city. So actually whatever necessary function is happening in the body let them happen, When I am going around walking around I have to look at the path, I can’t close my eyes and walk, so necessary functions have to happen but sarva-karmāṇi manasā

sannyasyāste – these are necessary functions happen in the body, indriya indriyarthesu, necessary contact between senses and sense objects has to happen but beyond that I will not be emotionally involved, I will not think that the contact between senses and sense object will lead me to happiness sannyasyāstesukhaṁ vaśī – It is like when a person watches TV understand that TV will not make me happy, so TV may go on but the person is not involved. Like that things will go on at material level but if we are renounced we will not become bound. So this is what Sri Krishna is telling naiva kurvan na kārayan, you will not be the doer and you will not make others do also.

Now Sri Krishna is telling Arjun to fight, so what is the meaning of I am not doer in making you do things? So Krishna is telling Arjuna you have a Kshatriya body and Kshatriya body will act according to nature and that nature is nature of fighting, so you can resist the nature but don’t become so identified with the nature that you become consumed by it and you identify yourself entirely Kshatriya, so Arjun is a soul but the soul is right now in Kshatriya body so the body has to function as Kshatriya and if Arjuna try to reject that and say I will act as a Sanyasi it will not work, for body is having certain way of working, at the same time if Arjuna entirely identifies as the Kshatriya conception then it will become bodily conception and one can’t make much spiritual advancement, so one must understand that you have a particular body and when you have particular body you have to work in a particular way but don’t become bound with that conception naiva kurvan na kāraya, So I am not simply telling you to do thing, I am telling you to act according to nature but act in such way that you are not emotionally involved, so that you will not get entangled karmically and that way you will stay free from bondage. And you will keep moving forward in your spiritual journey. So naiva kurvan na kārayan,

So here Sri Krishna is telling, “act Arjun” but “act without principle of bondage” i.e. “act without principle of entanglement.” So now Sri Krishna continues this thread of thought in the next verse.