I will tell you a story.
It is about the divine origin of Hatha Yoga.
One day Parvati, the consort of Siva, looked down on her children, human beings, and seeing them in such a bad way, asked her divine husband: « My Lord isn’t there anything that can be done to ease the suffering of our children? » Siva closed his eyes, entered into a state of deep meditation and started to teach the science of Hatha Yoga. Divine knowledge was pouring out of his lips as naturally and effortlessly as the Ganges flows to the sea...
When he had finished, he opened his eyes and discovered that Parvati had fallen asleep. As he had been teaching from this deep state of meditation, he could not remember what he had said. «What a waste!» said Siva to himself. Fortunately, in a pond nearby, there was a very special fish who had listened with great attention to the whole discourse. He said to Siva: «Please, do not worry my Lord, I remember everything!» Siva was so happy that he instantly liberated this great soul who had been the first recipient of this knowledge. He became Matsyendranath. Matsyendranath handed it over to his disciple Goraknath, and this started a lineage of siddhas, perfected beings.
This story underlines the fact that Hatha Yoga is a divine gift traditionally transmitted from Guru to disciple. In this lineage, the first Guru was Siva himself. Far from being frozen knowledge and codified instructions, it is a science kept alive by the yogis who have mastered it and who in turn transmit their knowledge to their deserving students. Sampoorna Hatha Yoga is a continuing expression of this tradition. That is why it is so effective for evolution of practitioners.
Hatha Yoga is Kundalini yoga
Of all the paths of yoga, Hatha Yoga is certainly the most well known. In its genuine form, it is a complete science for reaching perfection. As it deals with Sakti, the cosmic energy, it belongs to the tantric tradition, which focuses on the Divine Mother in the form of energy. This whole system is meant to lead the practitioner step by step to the highest stage of evolution by reawakening the energy which lies dormant at the base of the spine, the Kundalini Sakti and bringing it back to its original state of union with the Supreme Consciousness. So in that aspect, every Hatha Yoga practice – whatever label placed on it – is Kundalini yoga.
For the Kundalini Sakti to be reawakened and the Prana to flow freely through Sushumna, the mind and the nadis have to be purified. This involves an intense discipline, requiring faith, devotion, enthusiasm, as well as correct instructions and proper guidance from a knowledgable Guru. When all these elements come together in a pure form, the pathway to self-realisation, the union of Siva and Sakti, is prepared. Then the Soul can express itself in its pure and full state. Few people today are ready to undergo such intense discipline!
Extract from Yogi Hari's book "Sampoorna Yoga"