Mastery over oneself is vital for everyone. It is rightly said that "True superiority does not consist in being superior to others but in being superior to our former selves." Self-control consists in disciplining the mind and the senses. Sri Krishna teaches in the Bhagavad Gita (3.41) that self-control is a fundamental discipline for all seekers. If we allow the senses to have free rein, even success in secular life will prove elusive. Success in spiritual life certainly calls for self-mastery.
Eating, sleep, fear, and the urge to procreate are common to human beings and animals. The distinguishing trait of human beings is their power of discrimination and the resulting practice of detachment. The senses are vigorous and powerful and eagerly pursue sense objects. Even a single uncontrolled sense can destroy our discrimination and lead us astray.
In the Vivekachudamani (76) Sri Shankaracharya describes the plight of those whose senses are unrestrained: "Attachment to any of the five senses is enough to cause death, as happens with the deer, the elephant, the moth, the fish, and the bee. What then to speak of man, who is attached to all the five!" A deer meets with death when, unmindful of the danger lurking behind, it stands transfixed listening to sweet music. A mighty elephant wandering at will in the forest gets caught when tempted with the touch of a female elephant. A moth is attracted to a bright flame and rushes into it to burn and perish. A fish succumbs to taste by swallowing a piece of flesh used as bait on a hook. Attracted by the fragrance, a bee enters a lotus and gets trapped in it when the flower closes its petals at sunset. How then to describe the plight of man who, enslaved by all the five senses, loses the power to discriminate and is unable to strive for the spiritual goal.
"When food is pure the mind becomes pure," teaches the Chandogya Upanishad (7.26.2). Sri Shankaracharya explains that food means anything taken in through any of the five senses. Equally important are the ideas we absorb through the mind. None can carelessly continue to gather mental dirt and yet hope to discipline and focus the mind. "A disciplined mind acts as our friend, and an undisciplined mind acts as our enemy," teaches the Bhagavad Gita (6.6).
But how do we discipline the mind? Filling the mind with noble thoughts and continually dwelling on them disciplines and strengthens the mind. A devotee of God finds that sincere and steadfast repetition of the divine name restrains the mind and the senses without much effort.