Meditation is not concentration ... from the book by Osho..

MEDITATION is not concentration. In concentration there is a self concentrating and there is an object being concentrated upon. There is duality. In meditation there is nobody inside and nothing outside. It is not concentration . There is no division between the in and the out. The in goes on flowing into the out, the out goes on flowing into the in. The demarcation, the boundary, the border, no longer exists. The in is out, the out is in; it is a no-dual consciousness.

Concentration is a dual consciousness; that's why concentration creates tiredness; that's why when you concentrate you feel exhausted. And you cannot concentrate for twenty-four hours, you will have to take holidays to rest. Concentration can never become your nature. Meditation does not tire, meditation does not exahaust you. Meditation can become a twenty-four hour thing - day in, day out, year in, year out. It can become eternity. It is relaxation itself.

Concentration is an act, a willed act. Meditation is a state of no will, a state of inaction. It is relaxation. One has simply dropped into one's own being, and that being is the same as the being of All. In Concentration the mind functions out of a conclusion: you are doing something. Concentration comes out of the past. In meditation there is no conclusion behind it. You are not doing anything in particular, you are simply being. It has no past to it, it is pure of all future, It what Lao Tzu has called wei-wu-wei, action through inaction. It is what Zen masters have been saying: Sitting silently doing nothing, the spring comes and the grass grows by itself. Remember, 'by itself - nothing is being done. You are not pulling the grass upwards; the spring comes and the grass grows by itself. That state - when you allow life to go on its own way. When you don't want to give any control to it, when you are not manipulating, when you are not enforcing any discipline on it - that state of pure undisciplined spontaneity, is what meditation is. 

Meditation is in the present, pure present. Meditation is immediacy. You cannot meditate, you can be in meditation. You cannot be in concentration, but you can concentrate. Concentration is human, meditation is divine.