Consciousness and Energy
At the very beginning, there was no creation in universe. It was just pure Consciousness or Emptiness or Shi-va in its unmanifest form.
A desire to multiply and experience itself causes a Spandana or Vibration. This Primal Energy of the Cosmos is known as MahaPrana or Cosmic Prana or Shakti.
The whole Cosmos as it exists today, with different forms of creation are just modifications of this basic principle of Consciousness & Energy or Shi-va and Shakti.
Only difference being that each form of creation is at different level of evolution of Consciousness.
It is said Consciousness sleeps in rocks, dreams in plants, begins to awaken in animals and can be fully realized in a human being.
Macrocosmos and Microcosmos
Human Mechanism is a Micro Cosmos, a direct reflection of the Macro Cosmos i.e. the Universe.
For example, modern science says that 99% of universe is Empty Space and 1% is occupied by matter (Planets, Stars etc.).
In an atom, 99% of an atom is Empty Space and 1% is occupied by matter i.e. Atomic Particles.
Thus, there is a 1–1 correspondence between building block of matter i.e. an Atom with that of the Universe.
Human Mechanism – Doorway to Cosmos
The Human Body has records of every event of the cosmos from the start of Big Bang till now.
Through practice of Yoga, one can get into a state of Inner Realization and know the working of the Human Mechanism.
Comparing the design of the Human Mechanism with that of the larger Cosmos, it can become a doorway to knowing the whole Cosmos.
Ida and Pingala Nadi
In the Human Mechanism, Individual Consciousness manifests as Mind and flows as Mental Energy in Ida Nadi. MahaPrana manifests as Prana and flows as Pranic Energy in Pingala Nadi.
These two Nadis provide Consciousness and Energy to each and every cell of the body. And, form the basis of science of Hatha Yoga.
So, Hatha Yoga is not a physical exercise but a Science of knowing the Human Mechanism, a key to exploring the Cosmos.