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. In this way they should cooperate for the ultimate benefit of life, just like in our body there is the head, there is the arm, there is the belly and there is the leg. So we are all cooperating for upkeep of the body. Similarly, if either as a brāhmaṇa or as a kṣatriya or as a śūdra we keep up in mind that we have to serve Kṛṣṇa, then in either position we can become perfect. That is confirmed in many places.