The Blessed Lord said, “brahmana-ksatriya-visam
sudranam ca parantapa
svabhava-prabhavair gunaih – O scorcher of enemies – parantapa, the duties – karmāni of the Brāhmanas, the Kshatriyas and the Vaisyas – brāhmana-ksatriya-visām, as also of the Sudras – sudrānām have been fully classified – pravibhaktāni according to the gunas – gunaih born from Nature – svabhāva-prabhavaih.
samo damas tapah saucam
ksantir arjavam eva ca
jnanam vijnanam astikyam
brahma-karma svabhava-jam – The natural duties of the Brāhmanas – svabhāvajam brahma-karma are the control of the internal and external organs, austerity – tapah, purity – saucam, forgiveness – ksāntih, straightforwardness – ārjavam, knowledge – jnānam as also wisdom – vijnānam and faith – āstikyam.
The natural duties of the Ksatriyas are heroism, boldness, fortitude, capability and also not retreating from battle, generosity and lordliness.
The natural duties of the Vaishyas are agriculture, cattle-rearing and trade. Of the Sudras, too, the natural duty is in the form of service.
sve sve karmany abhiratah
samsiddhim labhate narah
yatha vindati tac chrnu – Being devoted to his own duty – sve sve karmani abhiratah, man – narah attains – labhate complete success – samsiddhim. Hear – srnu that – tat as to how – yathā one devoted to his own duty – sva-karma-niratah achieves – vindati success – siddhim.
[Chapter 18, Slokas 18.41 – 18.45]
Lord Krishna in the above verses reveals the rightful duty that one should engage in based on the classification of the gunas that are the natural actions befitting that classification.