The ultimate aim of yoga, as the name itself suggests is union. However there can be partial or complete union and there are and must be different paths to that union. By partial union is meant either a state of union that is yet not established firmly enough to be a realisation which is a permanent thing. Or else it is a union with one or the other aspect of the Divine such as the Impersonal or Personal or cosmic or Transcendent or Immanent Divine. The traditional yogas generally speak of union of the soul (Atma) with the Divine (Paramatma). there are variations of course but this is the final aim, the union of soul with the Supreme leading to a cessation of the cycle of birth and death and rebirth which is seen as a bondage to suffering and pain.
In Sri Aurobindo’s yoga the aim is not only the union of the soul with the Divine Mother but also of our nature with the Divine Force and Light and Power and Love and Wideness and Ananda. Union of the soul with the Divine Mother makes us fully conscious of being always a part and parcel of Her. By this we become not only liberated from ignorance but also from the fear of birth and death and rebirth. There is no more any need of a separate moksha since within life itself we have discovered moksha. If the Mother wants we shall come again and again; if She wants us to rest we shall rest forever in Her. The second union, that is to say the union and consequent liberation of nature brings another kind of freedom and perfection, – that of the very instruments through which the soul expresses itself or at least tries to. It means a transformation of our mind into a Mind of Plenary Light, of heart into a wide and beautiful space of Divine Harmony, Sweetness and Love. It means the transformation of our restless life and its troubled members into Luminous Force and Joy. It means the transformation of the very body into a vessel and vehicle of the Divine Peace and Beatitude and Light and Bliss. This later part is of course the more difficult part as it involves a long and patient working. Yet this takes place as the Mother’s Force descends into the adhar (mind, life and body) thereby opening each of the celestial centers or chakras in the course of streaming downwards. Since this takes place generally after the psychic being has stepped in front and nature is made ready to receive this influx through aspiration, rejection and surrender this tremendous pressure is borne slowly and steadily until the change begins to take place in each and every part. This is the process of opening of the chakras in this yoga from above downwards and after the soul has stepped in front. the purpose of this opening of the chakras is to allow Her Force to pour without hindrance through the channels meant for the flow of subtle energies (the chakras and the nadis are precisely that) and then spread outwards into the instruments built by nature such as the brain, heart, liver and organs and tissues etc. The chakras open by themselves as a result of the descent of the Mother’s force, often felt as heaviness over head in the beginning and then a thrill passing down the whole body.
In traditional kundalini yoga the chakras are opened from below by raising the Kundalini shakti (which is one form of the Mother’s Force that is involved in the base of spine in man and hidden in matter in general. It is raised here through will and concentration assisted by an elaborate system of Beej Mantras for each of the centers, this process can be dangerous as it means an opening of the lower centers such as those of food, sex etc. before climbing upwards (described very well by Pandit Gopinath Kaviraj). Hence it requires special close contact with the Guru who can control the energies as they stream upwards into the inadequate human system. This goes on until the Force is raised sufficiently enough so as to pass on through the skull and merge into the Supreme. There is no conception of transformation here and the energies raised at each level are of the same nature as the normal man except for being aggrandised and hence much more powerful with certain powers that are not ordinarily accessible. Hence all genuine gurus (very few if any now) ask the disciple to be prepared thoroughly through an elaborate process of purification with yamas, niyamas, pranayama, asanas etc. This purification is done in our yoga through the emergence of the psychic which is not known in the traditional kundalini yogas. However in most cases what is experienced is not the original Kundalini but something of it or of the vital energies that rise up like a vapour rising from heated water. It is rare for the true kundalini experience to take place and it can be very unsettling.
All this is avoided in this yoga as it opens from above downwards, the higher aspects of nature such as the mind and heart opening before the working begins on the lower vital and physical centers.