Bhagavath Yamunacharya says:
In the second chapter, it was told that one has to do the karma-yoga and control his sense organs and mind (manas). Then he has to do the jgnyaana yoga. At this point, one may object the need to do the karma yoga in those cases where he can do directly jgnyaana yoga. The objection is overruled here that the jgnyaana yoga cannot be even initiated if karma yoga is not done. The karma yoga has to be done as per the Saatvika tyaaga described earlier. By doing karma like this, one has to invoke the mercy of the Lord Sriman Narayana Paramaatman. By His grace, the jeevaatma's sins gets washed away. Only after this, the mind of the jeevaatma gets stabilized and clear. After conquering evil things like anger, enmity, desire etc., he gets his sense organs controlled and hence the mind. Only after this level of mental maturity, the jeevaatman can initiate the jgnyaana yoga. Therefore, karma yoga is mandatory for those who want to initiate jgnyaana yoga. The jeevaatman cannot do jgnyaana yoga without doing karma-yoga as told in the second chapter.
Further, the jeevaatma cannot stay away from doing karma except during the pralaya. The jeevaatman always does some or other karma stimulated by the prakruthi, which has satva-rajas and tamas attributes. The karma-yoga is not only less difficult but also ideal. Without doing karma, the jeevaatma cannot progress even in his material life. As this is the importance of karma-yoga, Bhagavan Shree Krishna Paramaatman addressed Arjua:
The karma-yoga has to be done only for the satisfaction of the Lord Shree Krishna Paramaatman. It should be "nishkaamya", meaning karma-yoga must be done without anticipation of results.
The jeevaatman who realizes that he is different from the body, does the karma yoga with Satvika tyaaga: That is, one has to sacrifice the ego "I am the doer of karma", "I am the enjoyer of its results" and the "Results are mine". But he should never sacrifice the karma itself. One has to do his karma, which is prescribed in the Saastra, without fail. One must realize that he is just instrumental in doing the karma and Bhagavan Shree Krishna Paramaataman is his only support, controller and Lord who has all the jeevaatmans and the insentient entities as instruments for his sport.
Bhagavan Shree Krishna Paramaataman stressed these aspects in the 3rd chapter of Gita and ordered Arjuna to get up and execute his duty properly.