Chapter 3 – Verse 4

न कर्मणामनारम्भान्नैष्कर्म्यं पुरुषोऽश्नुते ।
न च संन्यसनादेव सिद्धिं समधिगच्छति ॥

na karmanam anarambhannaiskarmyam puruso snute
na ca sannyasaanadeva siddhim samadhigacchati

purusha – a person
karmanam – of actions
anarambhat – by non-performance
naiskarmyam – the state of actionlessness
na asnute – does not gain
ca – and
sannyasanat eva – merely by renunciation
siddhim – liberation
na samadhigacchati – does not attain.

A person does not gain the state of action less by non-performance of actions. Nor does the person attain success out of mere renunciation.

As we saw in the verse before just by not doing an action or remaining action less and taking the short route, you are not going to get success. If one becomes a sannyasi without karma yoga how is one going to neutralize the raga dvesas? For a sannyasi there is no field out there to neutralize this, but for a karma yogi there is a field called this life which you are living as a Grahasta or vanaprastha.  Thus karma yoga becomes the means for gyana yoga and this in turn becomes the means for moksha.

Nyasa means renunciation and sannyasa means perfect or complete renunciation. Sarva karma sannyasa means renunciation of all actions and being in the form of knowledge acquired. We saw this in the previous chapter where Karma should be done with proper attitude without getting attached overly to results and taking the results with prasadah buddhi. 
For most people who take to this knowledge, it is not a predominant factor in their lives. They are interested in other activities and once they become interested in that, then the seeking of knowledge takes a back step. Such people are not sannyasi nor are ready yet mentally. Doing Karma is useful and should be done as it will prepare the mind slowly to grasp the subtle things that are required to understand the self.  Our mind has to become calm to grasp and focus on conducting atma vichara.

Suppose someone says that he or she has given up all passions and is says that he or she is a sannyasi. This is possible as slowly you can get disinterested and nothing else interests you.  Such a person sometimes says that ‘I have given up all desires, I am dispassionate etc.’. But the person still has the ego or Ahankara of the ‘I’. He or she has to give up that ‘I’ as well and this can be done through knowledge. You cannot give it up that easily as it is part and parcel of the ‘I’ which we all have. This goes away when one gets gyanam that I am not the doer and everything that is happening is due to the prakruti and my real nature is not these things or the actions. When such an attitude comes, then all karmas also disappear. 

Here the word naiskarmya is important as the state of actionlessness, freedom from action is identical to Moksha which is self-knowledge. It looks simple that by doing nothing you will get actionlessness and in turn you can get moksha. This is what Arjuna was thinking as by not fighting and doing nothing, he could attain moksha.

In the next verse, we will see that how even for a second we cannot remain without doing any action. Due to the nature of prakruti, we are always forced to do something or other.

The concept of renunciation is also explained by the following Thirukural.

Kural

தலைப்பட்டார் தீரத் துறந்தார் மயங்கி
வலைப்பட்டார் மற்றை யவர்.

Tamil Translation

அரைகுறையாக இல்லாமல் அனைத்தும் துறந்தவர்களே உயர்ந்த நிலையை அடைவார்கள். அவ்வாறு துறவாதவர்கள் அறியாமையென்னும் வலையில் சிக்கியவர்களாவார்கள்.

English Translation

Those who have entirely renounced (all things and all desire) have obtained (absorption into God); all others wander in confusion, entangled in the net of (many) births.