Ultimately, hatha yoga is a preparation for the body to contain the kundalini. Hatha yoga is what is done with this body to lead toward that realization of being this energy being. Energy has no weight, it occupies no space, it is invisible, yet what is happening is intensely dynamic, intensely alive. That is kundalini yoga.
When you perform your hatha yoga, do it with the awareness of these energies. Do not merely move muscles when doing hatha yoga. The muscles move anyway, but the purpose is to locate the field of energy.
People are not essentially a physical configuration. We are a pattern of energy channels, shakti-nadis, along which our physical body has arranged itself like iron filings along magnetic force lines, like straw floating on currents, eddies, whirlpools.
All that is physical is projected from and shaped by the patterns of subtler essences and currents. All that happens in the physical body is a manifestation of changes in the subtle body and in the energy channels. Only a part of what happens in the subtle body and in the energy channels is manifested on the physical plane. The chakras and nadis (energy channels) are co-incident with the plexuses and nerves but are not the same. They are flows, patterns and hub-centers in the circuitry of the subtle body. They are also connections and channels for the flow of forces from the causal body and above all they are energy currents and concentrations of the universal forces – prana (the vital force), chit (the consciousness force) and jiva(the life force).
Hatha yoga is essential as we learn to identify the subtler forces. As controls are established, the barriers begin to crumble ever so slowly. We need to whittle down tamas, the physical inertia of the body, by a constant process of purification through the practice of hatha yoga.
The practice of the physical aspects of yoga should be undertaken with a view to preparing the body in anticipation of changes that spiritual progress will require or induce. The practice of hatha yoga should not be overemphasized in isolation from general spiritual aims. To practice it only for health, beauty and longevity without any pursuit of deeper truths is to reduce yoga to the level of other physical sciences. As one progresses, hatha yoga practices at first help and then give way to kundalini yoga. Then an entry into the subtle body is gained. Hatha escorts one to this point and then bids adieu.