Sri Aurobindo
Letters of Sri Aurobindo
04. The Foundation of Sadhana
The difference between a vacant mind and a calm mind is this: that when the mind is vacant, there is no thought, no conception, no mental action of any kind, except an essential perception of things without the formed idea; but in the calm mind, it is the substance of the mental being that is still, so still that nothing disturbs it. If thoughts or activities come, they do not rise at all out of the mind, but they come from outside and cross the mind as a flight of birds crosses the sky in a windless air. It passes, 
disturbs nothing, leaving no trace. Even if a thousand images or the most violent events pass across it, the calm stillness remains as if the very texture of the mind were a substance of eternal and indestructible peace. A mind that has achieved this calmness can begin to act, even intensely and powerfully, but it will keep its fundamental stillness – originating nothing from itself but receiving from Above and giving it a mental form without adding anything of its own, calmly, dispassionately, though with the joy of the Truth and the happy power and light of its passage.