It will be evident that the two most important things here are the opening of the heart centre and the opening of the mind centres to all that is behind and above them. For the heart opens to the psychic being and the mind centres open to the higher consciousness and the nexus between the psychic being and the higher consciousness is the principal means of the siddhi. The first opening is effected by a concentration in the heart, a call to the Divine to manifest within us and through the psychic to take up and lead the whole nature. Aspiration, prayer, bhakti, love, surrender are the main supports of this part of the sadhana—accompanied by a rejection of all that stands in the way of what we aspire for. The second opening is effected by a concentration of the consciousness in the head (afterwards, above it) and an aspiration and call and a sustained will for the descent of the divine Peace, Power, Light, Knowledge, Ananda into the being—the Peace first or the Peace and Force together.
Ref : Letters on Yoga Vol. III