Sri Aurobindo translates Katha Upanishad, First Cycle: Third Chapter, Verses 3-9: “Know the body for a chariot and the soul for the master of the chariot: know Reason for the charioteer and the mind for the reins only. The senses they speak of as the steeds and the objects of sense as the paths in which they move; and One yoked with Self and the mind and the senses is the enjoyer, say the thinkers. Now he that is without knowledge with his mind ever unapplied, his senses are to him as wild horses and will not obey their driver of the chariot. But he that has knowledge with his mind ever applied, his senses are to him as noble steeds and they obey the driver. Yea, he that is without knowledge and is unmindful and is ever unclean, reaches not that goal, but wanders in the cycle of phenomena. But he that has knowledge and is mindful and pure always, reaches that goal whence he is not born again. That man who uses the mind for reins and the knowledge for the driver, reaches the end of his road, that highest seat of Vishnu.”
The imagery of the chariot and the charioteer to describe the relationship of the soul to the mind and the senses is a famous one that appears in both the texts of India and in the West. The verses here are very clear and straightforward and speak for themselves. It is important to note that the One is described as “yoked” with the Self and is the “enjoyer”. This underlines the Upanishadic view that there is one Spirit in the universe that is present both in the human being and in the rest of the manifested universe. The application of the powers of Reason, mind and the senses in furtherance of a dedicated life that eventually overcomes the bonds of death is highlighted as well. Those who are not heedful and who are constantly in a state of distraction are doomed to wander in the ever-changing landscape of the world of illusion, called variously maya or samsara.
Sri Aurobindo, The Upanishads, Katha Upanishad, pp. 213-241, and Kapali Sastry, Lights on the Upanishads, pp. 104-129