We have but one method of acquiring knowledge. From the lowest man to the highest Yogi, all have to use the same method; and that method is what is called concentration. The chemist who works in his laboratory concentrates all the powers of his mind, brings them into one focus, and throws them on the elements; and the elements stand analysed, and thus his knowledge comes.
The astronomer has also concentrated the powers of his mind and brought them into one focus; and he throws them on to objects through his telescope; and stars and systems roll forward and give up their secrets to him. So it is in every case — with the professor in his chair, the student with his book — with every man who is working to know.
You are hearing me, and if my words interest you, your mind will become concentrated on them; and then suppose a clock strikes, you will not hear it, on account of this concentration; and the more you are able to concentrate your mind, the better you will understand me; and the more I concentrate my love and powers, the better I shall be able to give expression to what I want to convey to you.
The more this power of concentration, the more knowledge is acquired, because this is the one and only method of acquiring knowledge. Even the lowest shoeblack, if he gives more concentration, will black shoes better; the cook with concentration will cook a meal all the better.
In making money, or in worshipping God, or in doing anything, the stronger the power of concentration, the better will that thing be done. This is the one call, the one knock, which opens the gates of nature, and lets out floods of light. This, the power of concentration, is the only key to the treasure-house of knowledge. The system of Raja-Yoga deals almost exclusively with this. In the present state of our body we are so much distracted, and the mind is frittering away its energies upon a hundred sorts of things. As soon as I try to calm my thoughts and concentrate my mind upon any one object of knowledge, thousands of undesired impulses rush into the brain, thousands of thoughts rush into the mind and disturb it. How to check it and bring the mind under control is the whole subject of study in Raja-Yoga.
Each one of us is engaged in some work, but the majority of us fritter away the greater portion of our energies, because we do not know the secret of work. Karma-Yoga explains this secret and teaches where and how to work, how to employ to the greatest advantage the largest part of our energies in the work that is before us. (II, 390 – 393)
Swamiji was gifted with the power of perfect concentration which used to astound people around. He had only to take up a book and scan the pages to get all the knowledge that was printed thereon, in which page, in what words and so on. This extraordinary ability of Swamiji surprised many a librarian in India and outside, whenever he used to take big volumes and return then in very short time.