"It is easy to concentrate the mind on external things, the mind naturally goes outwards; but not so in the case of religion, or psychology, or metaphysics, where the subject and the object, are one. The object is internal, the mind itself is the object, and it is necessary to study the mind itself - mind studying mind. We know that there is the power of the mind called reflection. I am talking to you. At the same time I am standing aside, as it were, a second person, and knowing and hearing what I am talking. You work and think at the same time, while a portion of your mind stands by and sees what you are thinking. The powers of the mind should be concentrated and turned back upon itself, and... this concentrated mind penetrate its own innermost secrets. Thus will we come to the basis of belief, the real genuine religion. We will perceive for ourselves whether we have souls, whether life is of five minutes or of eternity, whether there is a God in the universe or more. It will all be revealed to us. This is what Raja-Yoga proposes to teach."

- Swami Vivekananda, "Introductory" (Dec 14, 1895, New York Vedanta Society), Raja-Yoga, Complete Works: Vol 1