Q: Can one concentrate at one time on one centre and at another time on another or should one concentrate always consistently on the same centre?
A: As I have just said, there can be no harm wherever you concentrate, because concentration is only a means of giving up thoughts. Whatever the centre or object on which you concentrate, he who concentrates is always the same.

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Be as you are
The teachings of Sri Ramana Maharshi
edited by David Godman
a Penguin Book