Sri Aurobindo
Letters of Sri Aurobindo
Volume II - Part 2
A divine Name or a Mantra (like the So’ham) can enter the adhara and move in the breathing as in your experience. When it does so, that is not the opening of which I speak in the sentence you quote, but it may come to make the aspiration effective by helping in the opening – by removing something that prevents the opening and by leading to the experience it carries in it.
The experience to which the So’ham mantra leads is the 
realisation of one Being everywhere, all as the Divine, oneself and all as essentially one with that Divine. It is an experience in which one’s separate personal existence shut up in the body ceases to be the normal thing; one feels the body as a point or small thing in a vast existence, consciousness or Ananda that is the Divine and oneself as spread out in that vast consciousness – as if the world were within us and not we inside the world or as if the world were one with us and one with the Divine. It is the “cosmic consciousness” that comes by this mantra. For our Yoga this is a beginning only, not the end as it is in the ordinary Yoga,– a liberation, not the Siddhi.