Bhagavad Gita Verse 46, Chapter 18

yataha pravrittirbhootaanaam yena sarvamidam tatam |
svakarmanaa tambhyarchya siddhim vindanti maanavaha || 46 ||
 
From whom arises the origin of all beings, by which this entire creation is pervaded, having worshipped that through his duty, the person attains perfection.
 
yataha : from whom
pravrittihi : origin
bhootaanaam : of all beings
yena : by which
sarvam : entire creation
idam : this
tatam : is pervaded
svakarmanaa : his duty
tam : that
abhyarchya : having worshipped
siddhim : perfection
vindanti : attains
maanavaha : person
 
Shri Krishna says that we should submit the performance of our duty as an offering to Ishvara. Only then does it result in the samsiddhi, the foremost accomplishment, the perfection that was spoken of earlier. Otherwise, mere performance of our duty will result in merits and demerits, paapa and punya, which will further trap us in the cycle of samsaara. We have to inject bhakti or devotion to Ishvara into all our actions. In other words, karma yoga and bhakti yoga need to go together. Performance of duty with devotion to Ishvara reduces the ego, the gigantic bundle of likes, dislikes and fears which is an obstacle to liberation.
 
Even in our daily lives, actions performed with devotion to someone or something have a different kind of feeling. They allow us to channel energy that we never thought we had. A mother will work tirelessly, day and night, for the benefit of her children. Freedom fighters gave their lives for the service of the nation. Offering actions to Ishvara, however, has the effect of reducing the sense of enjoyership, the bhokta bhaava, the pursuit of actions driven by likes and dislikes. Selfless service reduces the sense of kartaa bhaava, the notion that the I has to perform an action to remove some incompleteness. We become instruments of Ishvara’s will, so there is no room for personal will.
 
Now, who is this Ishvara? He is the source, the origin of all beings, the intelligence cause, like the potter of a clay pot. He is also the material cause, the stuff by which everything is created, like the clay in a clay pot. When we offer our actions to the creator and sustainer of the universe, we lose all fear of the future, since we accept whatever comes our way as a prasaada, a gift from Ishvara. So there is no personal will, there is no personal preference, there is no fear. Doership, likes, dislikes and fears are nothing but the ego. It then, slowly withers away through karma yoga.

Bhagavad Gita Verse 17, Chapter 3

yastvaatmaratireva syaadaatmatruptashcya maanavaha |
aatmanyeva cha santushtastasya kaaryam na vidyate || 17 ||
 
But, one who revels only in the eternal essence, and is content and satisfied in the eternal essence, no duty exists for him.
 
yah : one who
tu : but
aatma-ratih : revels in the eternal essence
eva : only
syaat : remains
aatma-truptah : content in the eternal essence
cha : and
maanavaha : individual
aatmani : in the eternal essence
eva cha : and
santushtah : satisfied
tasya : for him
kaaryam :duty
na vidyate : do not exist
 
While hearing Shri Krishna extol the need to act in this world, many of us - whether we admit it or not - may want to know whether there is an exception to this instruction. In other words, are there any circumstances where do not need to perform actions anymore? Shri Krishna gives the answer in this shloka and the next.
 
If we examine ourselves, we realize that we derive pleasure and satisfaction from external sources: material objects, people, relationships and so on. Pleasant memories, which can be considered internal to us, do give us joy but were generated from some external source in the past. But, in reality, the source of happiness is the absence of desires experienced when we finally attain a material object.
 
For instance, if we want to buy a new shirt, a desire is created in the mind. Till such time that we get the shirt, we will be unhappy because of that desire. But once the desire is fulfilled, we experience happiness for a brief period of time. Is that happiness caused by the shirt, or by the temporary absence of desires? The wise person knows that it is the latter.
 
So in this shloka Shri Krishna makes a bold statement. He says that till we derive pleasure and satisfaction from things external to us, we have to act in this world. Conversely, one who no longer derives pleasure and satisfaction from external sources does not need to act in this world. He "revels" in the eternal essence which he has learned to recognize within himself. He no longer has to look outside for happiness.
 
Is there a contradiction here? Earlier it was mentioned that if one is human, one has to act. But here, it is mentioned that the realized individual does not need to act? The answer is that once that individual has understood the true source of happiness, he loses the sense of doership. In other words, the notion that "I am doing this action" goes away, and all his actions become natural and spontaneous.
 
As an example, if you truly love painting, and have mastered all the skills, then your painting becomes effortless and spontaneous. You experience a feeling that some people call "being in the zone". In fact, there may come a stage where you will feel that the hand is moving by itself, and the painting is happening on its own.
 
Similarly, all the actions of this wise individual become like that spontaneous painting.