One who has concentrated his mind, someway or other in Krsna, he has already attained the perfection of yoga. This is the substance of Krsna consciousness movement

Lecture on BG 6.30-34 — Los Angeles, February 19, 1969

Viṣṇujana: Verse thirty-four: “For the mind is restless, turbulent, obstinate and very strong, O Kṛṣṇa. And to subdue it, it seems to me, more difficult than controlling the wind (BG 6.34).”
Prabhupāda: Yes. Even if you can control the wind… That is not possible, nobody can control the wind. But even it is, theoretically accepting that you can control the wind, but it is not possible to control the mind. It is very difficult. Mind is so flickering and so turbulent. Go on.

Viṣṇujana: Purport: “Mind is so strong and obstinate, that sometimes it overcomes the intelligence. For a man in the practical world who has to fight so many opposing elements, it is certainly very difficult to control the mind. Artificially, one may establish a mental equilibrium toward both friend and enemy, but ultimately no worldly man can do so, for this is more difficult than controlling the raging wind. In the Vedic literatures it is said: ‘The individual is the passenger in the car of the material body and intelligence is the driver. Mind is the driving instrument, and the senses are the horses. The self is thus the enjoyer or sufferer in the association of the body and senses. So it is understood by great thinkers.’ Intelligence is supposed to direct the mind. But the mind is so strong and obstinate that it surpasses even one’s own intelligence, as an acute infection may surpass the efficacy of medicine. Such a strong mind is supposed to be controlled by the practice of yoga. But such practice is never practical for a worldly person like Arjuna. And what can we say of modern man? The difficulty is neatly expressed: ‘One cannot capture the blowing wind.’ And it is even more difficult to capture the agitated mind.”

Prabhupāda: Therefore this process, chanting Hare Kṛṣṇa, it captures the mind immediately. Simply if you chant, “Kṛṣṇa”, and if you hear, automatically your mind is fixed up in Kṛṣṇa. That means the yoga system is immediately attained. Because the whole yoga system is to concentrate your mind on the form of Viṣṇu. And Kṛṣṇa is the original personality of expansion of Viṣṇu forms. Kṛṣṇa is – just like here is a lamp. Now, from this lamp, from this candle, you can bring another candle; you can kindle it. Then, another, another, another – thousands of candle you can expand. In each candle is as powerful as this candle. There is no doubt about it. But one has to take this candle as the original candle. Similarly, Kṛṣṇa is expanding in millions of Viṣṇu forms. Each Viṣṇu form is as good as Kṛṣṇa, but Kṛṣṇa is the original candle, because from Kṛṣṇa everything expands.

So one who has concentrated his mind, some way or other in Kṛṣṇa, he has already attained the perfection of yoga. This is the substance of Kṛṣṇa consciousness movement. Go on. -vrindavana.net