Sva-dharma means one may be in goodness, one may be in passion, one may be in darkness, and one may be in mixture. So that is divided into four classes of men: the brāhmaṇa, kṣatriya, vaiśya and śūdra. So Bhagavad-gītā teaches us that anyone, if he worships the Supreme Personality of Godhead by sva-dharma, by his occupational duty, he also becomes perfect. For example, just like Arjuna. He was a military man, and his sva-dharma, his occupational duty, was to fight. So that fighting capacity he engaged himself in the service of Kṛṣṇa, and he became a devotee. Kṛṣṇa certified, bhakto 'si. What did he do? He did not chant Hare Kṛṣṇa mantra. Of course, he was chanting Hare Kṛṣṇa mantra constantly because he was thinking of Kṛṣṇa. He had no other business than to think of Kṛṣṇa. But by formality he did not become a Vaiṣṇava or chanting. But he was always thinking of Kṛṣṇa. Therefore he is certified as the foremost yogi. Yoginām api sarveṣām (BG 6.47).
So that is the trick—how we shall always think of Kṛṣṇa even we are engaged in our occupation duty. That will make us perfect. Actually, real sva-dharma is to be attached to Kṛṣṇa. Because we are part and parcel of Kṛṣṇa, but because we have got this material body, we have got this bodily concept of life. Therefore the Vedic injunction is divided that one class should be brāhmaṇa, one class should be kṣatriya, one class should be vaiśya, another should be śūdra.