The way of Yoga followed here has a different purpose from others,—for its aim is not only to rise out of the ordinary ignorant world-consciousness into the divine consciousness, but to bring the supramental power of that divine consciousness down into the ignorance of mind, life and body, to transform them, to manifest the Divine here and create a divine life in Matter. This is an exceedingly difficult aim and difficult Yoga; to many or most it will seem impossible. All the established forces of the ordinary ignorant world-consciousness are opposed to it and deny it and try to prevent it, and the sadhak will find his own mind, life and body full of the most obstinate impediments to its realisation. If you can accept the ideal whole-heartedly, face all the difficulties, leave the past and its ties behind you and are ready to give up everything and risk everything for this divine possibility, then only can you hope to discover by experience the Truth behind it.
The sadhana of this Yoga does not proceed through any set mental teaching or prescribed forms of meditation, mantras or others, but by aspiration, by a self-concentration inwards or upwards, by self-opening to an Influence, to the Divine Power above us and its workings, to the Divine Presence in the heart, and by the rejection of all that is foreign to these things. It is only by faith, aspiration and surrender that this self-opening can come.
Ref : Letters on Yoga Vol. II