This chapter explores Karma (action) and the four varnas that are divided, significantly, not just in terms of duty, but in terms of the manner in which that duty is executed. The crux of the chapter is revealed in Verse 18: Knowledge of reality has everything to do one’s view of Karma.
An Audio Course on Vedanta Texts- Bhagavad Gita: Bhagavad Gita (Chapter 4) by Swami Tattvavidananda Saraswati.