(Front cover of Bhagavad-gita As It Is, Macmillan edition, 1972)
Prabhupāda: There are many yogis, they perform yoga system or teach yoga system for some profit, but that is not the idea of yoga system. Everything should be engaged in the service of the Lord. Everything. Whatever we do, either as ordinary worker or as sannyāsī or as yogi, or as jñānī, all our energies should be dovetailed with Kṛṣṇa consciousness. That is real sannyāsa, that is real yoga. Ārurukṣor muner yogaṁ karma kāraṇam ucyate. Those who are just stepping on the staircase of the yoga system, for them, karma kāraṇam ucyate, they must work. In the beginning, nobody should stop working. Nobody should stop working.
Just like you'll find in the Bhagavad-gītā that Kṛṣṇa requesting Arjuna to become a yogi, but He never asked him to cease from the fight. How one can become a yogi, at the same time remain a fighter? That, a practical example you see. Kṛṣṇa is asking Arjuna, tasmād yogī bhavārjuna. "My dear Arjuna, therefore you become a yogi." But at the same time, He's asking to fight. Now, we know the yogi sits down at a place and meditates and concentrates his mind and controls his senses. How is that he is fighting, at the same time yogi? Huh?
This is the mystery of Bhagavad-gītā. You can remain a fighting man, at the same time the highest yogi, highest sannyāsī. How? In Kṛṣṇa consciousness. You have to fight for Kṛṣṇa. That's all. That is the secret. That is the secret. If you fight for Kṛṣṇa, work for Kṛṣṇa, if you eat for Kṛṣṇa, if you sleep for Kṛṣṇa, if you do everything for Kṛṣṇa, then you are the yogi, you are the sannyāsī, and you are everything. That is the secret of Bhagavad-gītā.
(Srila Prabhupada Lecture, New York, September 2, 1966)