Controlling the Mind & Intelligence

Kaṭha Upaniṣad (1.3.3–4):
ātmānaṁ rathinaṁ viddhi śarīraṁ ratham eva tu
buddhiṁ tu sārathiṁ viddhi manaḥ pragraham eva ca
indriyāṇi hayān āhur viṣayāṁs teṣu gocarān
ātmendriya-mano-yuktaṁ bhoktety āhur manīṣiṇaḥ


Here it is said that the living entity is the passenger riding in the chariot of the body, which is offered by material nature. The intelligence is the charioteer, the mind constitutes the reins controlling the horses, and the senses are the horses. Thus the living entity is the false enjoyer of the material world.
One who is advanced in Kṛṣṇa consciousness can control the mind and intelligence and in this way rein in the horses, the senses, even though they are very powerful. One who can control the senses by his mind and intelligence can very easily approach the Supreme Personality of Godhead, or Viṣṇu, who is the ultimate goal of life. Tad viṣṇoḥ paramaṁ padaṁ sadā paśyanti sūrayaḥ. Those who are actually advanced approach Lord Viṣṇu, their ultimate goal. Such people are never captivated by Lord Viṣṇu's external energy, the material world.