It is not enough to devote ourselves by the reading of Scriptures or by the stress of philosophic reasoning to an intellectual understanding of the Divine; for at the end of our long mental labour we might know all that has been said of the Eternal, possess all that can be thought about the Infinite and yet we might not know him at all. This intellectual preparation can indeed be the first stage in a powerful Yoga, but it is not indispensable: it is not a step which all need or can be called upon to take. Yoga would be impossible, except for a very few, if the intellectual figure of knowledge arrived at by the speculative or meditative Reason were its indispensable condition or a binding preliminary. All that the Light from above asks of us that it may begin its work is a call from the soul and a sufficient point of support in the mind. This support can be reached through an insistent idea of the Divine in the thought, a corresponding will in the dynamic parts, an aspiration, a faith, a need in the heart. Any one of these may lead or predominate, if all cannot move in unison or in an equal rhythm. The idea may be and must in the beginning be inadequate; the aspiration may be narrow and imperfect, the faith poorly illumined or even, as not surely founded on the rock of knowledge, fluctuating, uncertain, easily diminished; often even it may be extinguished and need to be lit again with difficulty like a torch in a windy pass. But if once there is a resolute self-consecration from deep within, if there is an awakening to the soul’s call, these inadequate things can be a sufficient instrument for the divine purpose.
Ref : Synthesis of Yoga