The japa is usually successful only on one of two conditions – if it is repeated with a sense of its significance, a dwelling of something in the mind on the nature, power, beauty, attraction of the Godhead it signifies and is to bring into the consciousness, – that is the mental way; or if it comes up from the heart or rings in it with a certain sense or feeling of bhakti making it alive, – that is the emotional way. Either the mind or the vital has to give it support or sustenance. But if it makes the mind dry and the vital restless, it must be missing that support and sustenance.
There is, of course, a third way, the reliance on the power of the mantra or name in itself; but then one has to go on till that power has sufficiently impressed its vibration on the inner being to make it at a given moment suddenly open to the Presence or the Touch. But if there is a struggling or insistence for the result, then this effect which needs a quiet receptivity in the mind is impeded. That is why I insisted so much on mental quietude and not on too much straining or effort, to give time to allow the psychic and the mind to develop the necessary condition of receptivity – a receptivity as natural as when one receives an inspiration for poetry and music.
[Sri Aurobindo. SABCL vol. 23, Letters on Yoga, Sadhana through Meditation, p 745]