Srimad Bhagavadgita Sadhaka Sanjivani -Swami Ramsukhdas
The Lord, in the thirty-ninth verse of the second chapter, said to Arjuna, "This is the wisdom of Sankhya given to thee, to attain equanimity, 0 Arjuna. Now listen; about equanimity to be acquired, through the Discipline of Action, in which a person by performing action for the welfare of others, without any selfish motive, attains equanimity." Than according to the context, in response to Arjunas question, Lord Krsna having described the marks of a man of steady wisdom, completes this topic.
At the beginning of the third chapter, Arjuna asked Lord Krsna "If You think that knowledge is superior to action, why do You urge me, to do this savage deed (war)?" In response to his question, the Lord, from the fourth to the twenty-ninth verses, lays emphasis on the performance of actions, by which a man attains equanimity. In the thirtieth verse, He says that surrendering all actions to Him, with a discriminative insight, free from desire and egoism he should perform actions without mental agitation. In the thirty-first and thirty-second verses, He declares the sweet fruit of following His preaching (explained in the previous verse) and the harm in not following it. In the thirty-fifth verse, He declares, "Better is death in one's own duty." In the thirty-sixth verse Arjuna asks, "By what is a man impelled to commit sin?" The Lord replies, It is desire, all devouring and most sinful, which is the enemy," and ordered Arjuna to slay this enemy.
Arjuna wants to renounce the performance of action, so he says to Lord Krsna, "Why do You ask me to be engaged in this savage deed?" Therefore, the Lord, lays special emphasis on the performance of duty, specially in the third chapter, while in the fourth chapter, He imparts knowledge about actions. He declares, "I shall teach thee such action, (the nature of action and inaction), after knowing which, thou shalt be liberated from evil (the wheel of birth and death) (4/16). This Karmayoga, in spite of being without beginning, was lost to the world through, a long lapse of time, because of the absence of scholarly teachers (sages), who could impart it. The Lord, in the first three verses, describing how Karnayoga was handed down from ancient times, proves how it existed from times immemorial.