The two serpents interlaced are the two channels in the spine, through which the Shakti moves upward and downward.
There is a Yoga-Shakti lying coiled or asleep in the inner body, not active. When one does yoga, this force uncoils itself and rises upward to meet the Divine Consciousness and Force that are waiting above us. When this happens, when the awakened Yoga-Shakti arises, it is often felt like a snake uncoiling and standing up straight and lifting itself more and more upwards. When it meets the Divine Consciousness above, then the force of the Divine Consciousness can more easily descend into the body and be felt working there to change the nature.
It seems to me that you must know by this time about the psychic being — that is behind the veil and its consciousness also; only a little comes out in the mind and vital and physical. When that consciousness is not concealed, when you are aware of your soul (the psychic being), when its feelings and consciousness are yours, then you have got the consciousness of the psychic being. The feelings and aspirations of the psychic being are all turned towards truth and right consciousness and the Divine; it is the only part that cannot be touched by the hostile forces and their suggestions.