Sri Aurobindo wrote this piece as a letter to Punamchand Shah on 19 August 1927. In 1928 it was published as the fifth chapter of The Mother. The full text is below.
If you want to be a true doer of divine works, your first aim must be to be totally free from all desire and self-regarding ego. All your life must be an offering and a sacrifice to the Supreme; your only object in action shall be to serve, to receive, to fulfil, to become a manifesting instrument of the Divine Shakti in her works. You must grow in the divine consciousness till there is no difference between your will and hers, no motive except her impulsion in you, no action that is not her conscious action in you and through you.
Until you are capable of this complete dynamic identification, you have to regard yourself as a soul and body created for her service, one who does all for her sake. Even if the idea of the separate worker is strong in you and you feel that it is you who do the act, yet it must be done for her. All stress of egoistic choice, all hankering after personal profit, all stipulation of self-regarding desire must be extirpated from the nature. There must be no demand for fruit and no seeking for reward; the only fruit for you is the pleasure of the Divine Mother and the fulfilment of her work, your only reward a constant progression in divine consciousness and calm and strength and bliss. The joy of service and the joy of inner growth through works is the sufficient recompense of the selfless worker.
But a time will come when you will feel more and more that you are the instrument and not the worker. For first by the force of your devotion your contact with the Divine Mother will become so intimate that at all times you will have only to concentrate and to put everything into her hands to have her present guidance, her direct command or impulse, the sure indication of the thing to be done and the way to do it and the result. And afterwards you will realise that the divine Shakti not only inspires and guides, but initiates and carries out your works; all your movements are originated by her, all your powers are hers, mind, life and body are conscious and joyful instruments of her action, means for her play, moulds for her manifestation in the physical universe. There can be no more happy condition than this union and dependence; for this step carries you back beyond the border-line from the life of stress and suffering in the ignorance into the truth of your spiritual being, into its deep peace and its intense Ananda.
While this transformation is being done it is more than ever necessary to keep yourself free from all taint of the perversions of the ego. Let no demand or insistence creep in to stain the purity of the self-giving and the sacrifice. There must be no attachment to the work or the result, no laying down of conditions, no claim to possess the Power that should possess you, no pride of the instrument, no vanity or arrogance. Nothing in the mind or in the vital or physical parts should be suffered to distort to its own use or seize for its own personal and separate satisfaction the greatness of the forces that are acting through you. Let your faith, your sincerity, your purity of aspiration be absolute and pervasive of all the planes and layers of the being; then every disturbing element and distorting influence will progressively fall away from your nature.
The last stage of this perfection will come when you are completely identified with the Divine Mother and feel yourself to be no longer another and separate being, instrument, servant or worker but truly a child and eternal portion of her consciousness and force. Always she will be in you and you in her; it will be your constant, simple and natural experience that all your thought and seeing and action, your very breathing or moving come from her and are hers. You will know and see and feel that you are a person and power formed by her out of herself, put out from her for the play and yet always safe in her, being of her being, consciousness of her consciousness, force of her force, ananda of her Ananda. When this condition is entire and her supramental energies can freely move you, then you will be perfect in divine works; knowledge, will, action will become sure, simple, luminous, spontaneous, flawless, an outflow from the Supreme, a divine movement of the Eternal.