Disciple: If I am Brahman, Why don't I always realise it?
Swamiji: In order to attain to that realisation in the conscious plane, some instrumentality is required. The mind is that instrument in us. But it is a non-intelligent substance. It only appears to be intelligent through the light of the Atman behind therefore it is certain that you won´t be able to know the Atman, the Essence of Intelligence, through the mind. You have to go behind the mind. The real fact is that there is a state beyond the conscious plane, where there is no duality of the knower, knowledge, and the instrument of knowledge etc. when the mind is merged, that state is perceived. I say it is "perceived" because there is no other word to express that state. Language cannot express that state.
Excerpted from the book
Meditation and Its Methods According to Swami Vivekananda