If a pebble in our boot torments us we expel it. We take off the boot and shake it out. Once the matter is fairly understood, it is just as easy to expel an intruding and obnoxious thought from the mind. About this there ought to be no doubt, no two opinions. The thing is obvious, clear and unmistakable. It should be as easy to expel an obnoxious thought from your mind as it is to take a stone out of your shoe; and till a man can do that, it is just nonsense to talk about his ascendancy and conquest over nature!
Benefits of Thought-Control
Thoughts lead to action. Thoughts are the sources of all actions. Thought is the real Karma. Thinking is the real action. If you can root out all evil thoughts in the beginning, you will not do any evil action. If you can nip them in the bud, you will be free from the miseries and tribulations of this world. Watch your thoughts with vigilance and introspection.
Thought is the real action. Activities of the mind are the real Karmas. Once the tossing of the mind vanishes, you will get good meditation. The mind will be very, very calm. Get rid of the impurities of the mind. Have mastery over the mind. Then all the miseries of the with births and deaths will come to an end. If you free yourself from the clutches of the mind, Moksha / Nirvana (liberation) will come by itself. There is no doubt about this.
A wise man watches his thoughts and eradicates all evil thoughts as they arise from the surface of the mind. So he is happy. He has always pure thoughts. By meditation on God, pure thoughts emanate from the mind, because God is purity.
If you have control over your thoughts, you can turn out immense work with intense concentration. Mental torments of all sorts, cares, worries and anxieties will disappear. The peace that you will enjoy cannot be adequately described.
Those who have even a little control over their thoughts and speech will have a calm, serene, beautiful, charming face, sweet voice and brilliant, lustrous white eyes. Just as sweet perfume continuously emanates from an incense stick, so also divine perfume and divine effulgence (magnetic, aura) radiate from a Yogi who has controlled his thoughts and who is constantly dwelling on Brahman or the infinite. The effulgence and perfume of his face. When you hold in your hand a bouquet made of jasmine and rose flowers, the sweet perfume pervades the whole hall and tickles all alike. Even so, the perfume of fame and reputation of a Yogi who has controlled his thoughts spreads far and wide. He becomes a cosmic force.
Radium is a rare commodity. There are only 16 grains in the world. Yogis who have controlled their thoughts are also very rare in the world, like radium.
Mind – Its Mysteries and Control by Sri Swami Sivananda