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.

There is nothing wrong with God's creation. Mystery and Suffering only exist in the mind.

The Self is the heart, self-luminous. Illumination arises from the heart and reaches the brain, which is the seat of the mind. The world is seen with the mind; so you see the world by the reflected light of the Self.

The solution to your problem is to see who has it.

To ask the mind to kill itself is like making the thief the policeman. He will go with you and pretend to catch the thief, but nothing will be gained. So you must turn inward and see where the mind rises from, and then it will cease to exist.

Peace can reign only where there is no disturbance, and disturbance is due to thoughts that arise in the mind.

Bliss is a thing which is always there and is not something which comes and goes. That which comes and goes is a creation of the mind.