When he has gone through some training in yoga or meditation, he is fit to ascertain Truth . . . emotionally and mentally fit. His mind can be held for a long time on a single theme without wandering; he can concentrate his thoughts upon the pursuit of Truth to the exclusion of everything else. His power of attention is made needle-sharp and brought under control. Thus equipped, he can begin to find Truth.
Everything up till now was but preparation. With this extraordinary sharpness of intelligence and attentiveness, he has next to discriminate between pure Consciousness per se, and everything that merely forms the content of consciousness. For Consciousness is the ultimate, as science is beginning vaguely to see. With concentrated, sharpened mind he can pierce into his deepest self and then endeavour to understand it; he can also pierce into the external world of matter and understand that too. Unthwarted by the illusions of the ordinary man, who takes what his eyes see for granted, he can probe beneath appearances. And when he can at last see the Truth, his spiritual ignorance falls away of its own accord and can never come back to him again, any more than a man who has awakened from dreaming can relapse back into his original dream.
Thus, the actual finding of Truth, which is the same as Nirvana, Self-Knowledge, Liberation, is really a work of brief duration--perhaps a matter of minutes--whereas the preparation and equipment of oneself to find it must take many incarnations.
If this presentation sounds unorthodox, he will find that in chapter 13, verse 2, of the Bhagavad Gita, Krishna distinctly asserts that both the knowledge of the Kshetrajna and Kshetra are required before a man may be deemed to possess the truth. In plain English, this merely means that he must know both himself and his body. But as the body is a part of the external physical world and represents it in miniature, the meaning must be extended to include the whole physical world. Merely going inwards and enjoying emotional ecstasies will not do. It may make him happy, but it does not give the whole truth. He has to come outside again, and lo and behold! there is the material world confronting him--yet not understood.
If however, the yogi takes his sharpened, concentrative mind and applies it to such understanding, he discovers that the world of matter is ultimately space and that all material forms are merely ideas in his mind. He discovers, too, that his inmost self is one with this space, because it is formless. He perceives the unity of all life and he has found Truth, the whole Truth. This is maha-yoga, the higher path that awaits every yogi or mystic, and which alone leads to Truth.
-- Notebooks Category 2: Overview of Practicies Involved > Chapter 9: Conclusion > # 63