To be able to receive the Divine Power and let it act through you in the things of the outward life, there are three necessary conditions:
(i) Quietude, equality—not to be disturbed by anything that happens, to keep the mind still and firm, seeing the play of forces, but itself tranquil.
(ii) Absolute faith—faith that what is for the best will happen, but also that if one can make oneself a true instrument, the fruit will be that which one’s will guided by the Divine Light sees as the thing to be done—kartavyam karma.
(iii) Receptivity—the power to receive the Divine Force and to feel its presence and the presence of the Mother in it and allow it to work, guiding one’s sight and will and action. If this power and presence can be felt and this plasticity made the habit of the consciousness in action,—but plasticity to the Divine force alone without bringing in any foreign element,—the eventual result is sure.
Ref: Letters on Yoga – II