The jiva born with a human body, is given to likes and dislikes, and gets ruled by likes and dislikes.
Instead of holding the rein which is the mind and controlling the horses in the form of the 5 senses, as the atma the controller or this body, who is given this free will to control ones own body mind and action, instead this person does not seem to be able to make use of his own free will given to him.
This person seeking joy, and finding joy in the enjoyment of ones own likes and avoidence of ones dislikes, becomes dependent therein upon the fulfilment of ones own likes and on the avoidence of what one dislikes.
Here he or she hits a two fold barrier.
One is that the world is not ready to give in to his own likes and dislikes so he finds out how extremely difficult it is to make the world bend to his whims and fancies.
He also discovers that his own likes and dislikes even when fulfilled happen to not give total fulfilment even under the most favourable conditions. Such as desires fulfilled through righteous means will mean the person is fully able to enjoy what he has rightfully earned, without any guilt necessarily intervening ( atleast unto his own knowledge), but even then the person finds that the joy from desire fulfilment is momentary and the wish now fulfilled, only gives lease for a fresh wish to take over, and a fresh desire to chase.
Thereby the person never finds oneself happy permanently and it appears a cycle of happiness and unhappiness.
Some people take the unhappiness to be a driver to again work and go for the next achievement.
Even that process is full of pains and pangs of sufferings, and there may be again that momentary happiness at the end of it. Again so much dependent on laws favoring one, and many times they may not favor the individual, based on his past karmas.
Meanwhile the individual is also uknowingly still attaining papa karmas along the way no matter how much dharmic he tries to be. Moreover there is anadi papa karmas that the individual has performed in the past, that is always going to chase him.
Adharmic route is not even a consideration as the person goeS against his own set of values that he holds dear unto himself . The person hence is not even available to receive the fruit so called of a desire fulfilled via an adharmic route , his so called joy is with a rajasic mind that has lost touch with the basic individual who seeks peace, thereby there is not possibility of peace for a person given to adharma and only more and more pain and ashanti is in store.
But a person agiven to likes and dislikes and unable to separate onself from it, eventually gets taken over by greed.
A like fed, doesnt go away, it becomes greed.
It creates attachement.
It also hides ones own sense of dharma and makes one take the wrong path, so leads to more greed and attachement.
Its a cycle which leads to destruction of the individual eventually.
So in order to free oneself from this likes and dislikes route in order to gain the happiness one seeks, there is the route of karma yoga.
it has a 2 fold advice .
YogaH karmasu kausalam.
Giving priority to ones duties, which are to be done, by making use of ones free will, and deliberately doing only ones duties, makes one understand that one indeed has a free will, that one can make use of, and one is the controller of ones own destiny and body mind, and is not at the mercy of any like or dislike.
This hence gives a chitta shuddhi. This duties are the work given by god to you, svadharma, so you are doing gods bidding. It is gods gift given to the individual to uplift himself and extricate oneself from the whirlpool of likes and dislikes and free onself from the samsara. So do your duty, with a thankful attitude to the lord for being present as the dharmica buddhi, and offer ones duties unto him as the lord the manager here, for whose sake you are performing your duties. Here you are assisting the lord in his task of running this universe, which he does effortlessly yet efficiently and effectively, with benevolence yet with total justice and beauty and harmony.
The other advice is samatvam yoga uchyate. So whatever the results god gives one, for ones actions driven by any kind of desire, even selfish desire, accept the fruits of the action, as one given by the lord. Accept it with grace, and an understanding that lord has given it to you, and he must have a reason for it, and I should accept whatever it maybe with grace and happiness, even if it is something I dont prefer or like.
So via this kind of attitude, I develop a relationship with the lord, and with this attitude that he recommends, I also gain the inner freedom. He also makes sure, "shastra shravanam" is listed as one of the duties.
So in his spiritual program he has included the most important component for my freedom , which is listening to mahavakya .
So mahavakya says I and the lord are one.
This karma yogi individual cannot be the lord with whom he is relating.
So here the oneness refers to the truth of the karma yogi individual.
The truth of the individual is that individual is of the nature of consciousness. The individual is in reality the consciousness itself, that appears as an individual.
What is the reality of the individual its none other than a witness consciousness. Due to ignorance, the individual with the body mind self complex, says I am this body.
The I am here, is actually pure consciousness that has no name form or limitations, is self existent, independent and devoid of any trace of any object or its properties. But due to ignorance, we have with body mind and ego, and individual who says I am this body mind, 'I' being all the time limitless egoless pure consciousness.
Now this same pure consciousness with the garb of ishvara, says, I am ishvara , and the entire universe is his body, and he the consciousness is the material cause and the intelligent cause being all knowledge, and being the magician who manifests all that is here, from within oneself, from unmanifest state to manifest state. Here also he is just pure consciousness.
So if we look at "I am" there is no difference.
Difference is in the name and form when we add 'individual', or 'total' as a suffix to "I am".
This I am is in fact not even ego, its is only in admixture with the name and form, there is an ego identifying with individual or total.
Pure I am, is just existence consciousness.