A Simile: The chariot, the charioteer, horses, reins and the rider
आत्मानँ रथितं विद्धि शरीरँ रथमेव तु ।
बुद्धिं तु सारथिं विद्धि मनः प्रग्रहमेव च ॥ ३॥
ātmānam̐ rathitaṃ viddhi śarīram̐ rathameva tu .
buddhiṃ tu sārathiṃ viddhi manaḥ pragrahameva ca .. 3..
Know the atman to be the master of the chariot; the body, chariot; the intellect, the charioteer; and the mind, the reins.
Swami Vivekananda Says —
(Verses 3 and 4)
This body, O Nachiketas, is the chariot, the organs of the senses are the horses, the mind is the reins, the intellect is the charioteer, and the soul is the rider in the chariot. When the soul joins himself with the charioteer, Buddhi or intellect, and then through it with the mind, the reins, and through it again with the organs, the horses, he is said to be the enjoyer; he perceives, he works, he acts.[Source]
Know that the soul is sitting in the chariot. The body is the chariot; the outer senses are the horses; and the mind the reins; and the intellect the charioteer. So man crosses the ocean of Maya. He goes beyond. He reaches God. When a man is under the control of his senses, he is of this world. When he has controlled the senses, he has renounced.[Source]