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.