What is Karma Yoga?
Karma Yoga is about performing right actions backed by appropriate knowledge and devotion. Knowledge and Devotion are the wheels on which the cart called Karma moves. While Knowledge and Devotion are the most important components, Karma is the primary means to gain Knowledge and reach the goal. Hence this Yoga is called Karma Yoga. Is is about transforming all our actions into service, not being attached to fruits of actions and being equipoised to their outcome.
Why Karma Yoga?
Humans are action centric. It is very well known that no one can stay even for a second without performing any action. Arresting all action is impossible. At the same time, actions bind the soul to this material existence if they are done without mastering the art of performing them. Kama Yoga teaches this art of performing actions.
By practicing Karma Yoga, one can perform actions but still keep onseself untainted by them. This is lot easier and highly fruitful than attempting to forcibly withdraw onseself from all actions altogether.
Jnana and Bhakti Yogas
The other two alternatives to Karma Yoga are Jnana Yoga and Bhakti Yoga. These tow are at a very higher pedestal. They involve transgressing the limitations of Karma and continuous experience of the ultimate reality. By this, it should not be mistaken that Jnana Yoga and Bhakti Yoga do not have any Karma component. In fact, the magnitude of Karma in Jnana Yoga and Bhakti Yoga is for more than that of the Karma Yoga. But the magnitude of Knowledge and Devotion respectively, are much much higher than their Karma counterpart in these two yogas. For this reason, these two paths are simply beyond the human capacity. Hence the message of Lord Sri Krishna in Bhagavad Gita to all humans is to become Karma Yogins.
Atmopasana
Atmopasana is the central teaching of Shrimad Bhagavad Gita that has a universal appeal and an eternal applicability. It is also the central theme of the Vedas, the Upanishads and a host of other Holy Scriptures. It is the highest form of spiritual practice that bestwos the supreme knowledge of Brahman. It is exactly "The Karma Yoga" prescribed by Lord Sri Krishna. It is the Yoga of the Yogas or the King of the Yogas. This is that Adhyatma Yoga, instilled in which, the seeker crosses the states of mundane joy and sorrow and opens the gateway of spiritual realization.
The Supreme Brahman is an ocean of infinite qualities. No one can fully comprehend all of his qualities. As per the Holy Scriptures, humans can contemplate mainly upon four aspects of Brahman viz., Sat, Chit, Ananda and Atma.
Among these four, the Atma ascpect is the most basic, most important and the core concept. It is also the seed component of all the other three. The Sat, Chit and Ananda easpects convey that the Supreme Brahman is the owner or Swami (Atma) of these qualities. In other words, the Atma aspect can be clearly seenn to be an inherent component of all the other aspects as well.
Any contemplation is incomplete without the inclusion of this Atma aspect in it. Atmopasana is the most recommended practice as it involves contemplating upon this very important aspect of the Brahman.
Evey human being is a part of the enternal Wheel of Nature. Human life depends on this Wheel of Nature for its very existence and survival. Hencem it owes something back to the Wheel of Nature. It is mandatory for everyone to contribute towards the smooth functioning of this wheel in his/her own capacity. This is possible by performing right actions that contribute towards protecting the environment, protecting the natural resources and empowering the spiritual energies that maintain the Nature Wheel as enjoined in the Holy Scriptures.
Atmopasana is about performing right actions with Atma Consiousness. Atma Consiousness is the way of complete surrender to the Supreme Atman and willfully performing right actions fully realizng that He is the stimulator, controller and the master of all our actions and the actions of everyone else.
The essence of Atmopasana can be succintly given as follows -
The Supreme Lord, who is the fulfiller of all desires, is hailed in all Holy Scriptures. Performance of actions in expectatin of mundane material benefits is not their real puport. Realizing this fact, one should perform right actions, remembering, at all times and places that the supreme Brahman, the one who is full of auspicious qualities, is his master and the master of all. - Translation of the words of Sri Raghavendra Swami in his Gita Vivrutti.