There are six ways, I think, through which you can attain freedom. What we speak of here is a very direct way: It is called Brahma vidya - direct awakening. There are also other ways, like pranayama and there is yoga; there is kundalini; and there is also bhakti yoga. All these methods are useful.
Whatever is suitable to you - whatever you like - you can succeed with. What we mostly speak here is Brahma vidya, direct awakening through vichar - reason. We look objectively at how to arrive at purusha, the absolute truth which is one without a second, unchanging.
Whatever changes is not real. Starting with the body it changes, from childhood to youth to old age to death it changes. Even the whole world changes with earthquakes, with cyclones. The world which was here a hundred years ago or a thousand years ago is not now. Even money changes, and whatever changes is not the truth. The mind is also changing. Sometimes it is peaceful, sometimes it is restless.
The mental states that you pass through every day also change. We have a firm belief that what we see in the waking state is real. This reality disappears in the dream state. Both waking and dreaming disappear in the sleep state, and sleep also disappears in the next waking state.
What is alternating is not real. This is a fact.
Whenever there is a change there must be an underlying substratum which does not change, on which these changes are taking place. When you see a clay jar, instantly you have a consciousness of earth. When you see a ring, instantly you are conscious of gold. When you see a table, instantly you are aware that it is a wood. Like this there must be some substratum which has taken a different shape and a different name. Whatever changes has a substratum.
Whatever you can objectify and externalize, do it. Finally you will reach the body itself. Whatever you see must be external to you. If you see the body it is external, and something must be internal - something must be inner. That is why you can see things; because whatever you see must be external, must be an object. Even in a dream everything is external to you. There are mountains, there are rivers, men, trees; all are external to you. The sleeping man is not affected by the dream, he is only seeing.
So now we are advised to discover the changeless on which these changes are taking place. How is this to be done? By rejecting. Whatever changes, reject it. Sit down coolly for some time and see. Whatever you see, whatever you perceive or conceive or feel can be rejected. Something will be left which you cannot reject. That is the permanent abode of existence, consciousness, bliss and freedom.
This can be done instantly or this may take ages.