‘We human beings live between the two realities of earth and sky. The earth stands for all that is practical, material, tangible, and incarnate. It is the knowable world, objectively knowable through voyages of discovery and observation. We all partake of this world and its knowledge through the vast store of accumulated collective experience. There is one word for all this. It is Nature. In Sanskrit, Nature is called Prakrti. It is composed of five elements, which we characterise as earth, water, fire, air and space. Consequently and sympathetically, the body is made up of these same five elements, which is why we also use the term prakrti for the body. When space explorers bring back rocks from the moon and scientists study them, they are studying Nature. When we calculate the temperature on the surface of the sun, we are observing Nature. Whether we study planetary Nature or cosmic Nature, it is Nature. We too are part of Nature, therefore constantly changing, so we are always looking at Nature from a different viewpoint. We are a little piece of continual change looking at an infinite quantity of continual change.
Even hundreds of years before Patanjali wrote the Yoga Sutras, Indian yogis were trying to see some pattern in the seemingly chaotic fluctuations of Nature. The infinite variety of natural phenomena gives an appearance of chaos, but, they asked, is it possible that the laws that govern the unending turbulence of nature are orderly and comprehensible? And if we can grasp how they work, would it not be possible for us to emerge from the chaos into order? All games are meaningless if you do not know the rules. When you do, they can become very good fun. You still take a few knocks and lose a few games, but at least you are participating; you are playing the game. Yoga says you are playing the game with the body and self. By playing you can learn the rules, and if you observe them, you have a far better chance of success in life as well as of gaining illumination and freedom.
So humankind stands with its feet planted squarely on the earth, as in Tadasana (mountain pose), and its head in the sky. But what then do we mean by the sky? Clearly I do not mean the earth’s biosphere, or anywhere that physically exists, however far away. I could have said, ‘Our feet on the earth and our head in the heavens.’ Many languages do not have two separate words for sky and heaven as English does. The word heaven is useful as it suggests something that is not physical. This opens up possibilities: a) That it is perfect, as nothing physical can be perfect since all phenomena are unstable; b) that is is Universal-i.e. One, whereas Nature is many as we see from its diversity; c) that it is Everywhere, Omnipresent since, not being physical, it is not limited or defined by location; d) that is is supremely Real or Eternal. In yoga the body is held to be of real substance, whereas the changing of ourselves and unveiling of the immeasurable sky within is called cit-akasha, or literally the vision of space itself.’
Light on Life, B.K.S. Iyengar