|Haidakhan Babaji meditating|
The effort to keep the mind always concentrated on Atman or Brahman is what is called Atma-Vichara.
Till the blissful Jnana dawns on you, you should do constant and intense Sadhana.
You must not stop thinking of Brahman (Brahma-Chintana) even for half a second, even for the time taken for one winking.
You must become Nididhyasana-Parayana (one whose sole refuge is meditation on OM with feeling and meaning). Then only Brahma-Jnana (direct knowledge of Brahman) is possible.
~ Swami Sivananda