Concentration is not thinking of one thing. On the contrary, it is excluding all thoughts, since all thoughts obstruct the sense of one's true being. All efforts are to be directed simply to removing the veil of ignorance. Concentrating the mind solely on the Self will lead to happiness or bliss. Drawing in the thoughts, restraining them and preventing them from straying outwards is called detachment (vairagya). Fixing them in the Self is spiritual practice (sadhana). Concentrating on the heart is the same as concentrating on the Self. Heart is another name for Self.

The search "Who am I"...ends in the annihilation of the illusory "I" and the Self which remains over will be as clear as a gooseberry in the palm of one's hand.

Let knowledge be guessed by the sign of equality to all beings.

The normal self is the mind. The mind is with limitations. But pure Consciousness is beyond limitations, and is reached by investigation into the "I."

The state of self-realization, as we call it, is not attaining something new or reaching some goal which is far away, but simply being that which you always are and which you always have been.

The Self is the one Reality that always exists, and it is by the light of the Self that all other things are seen.

You need not aspire for or get any new state. Get rid of your present thoughts, that is all.