In the West, the understanding of hatha yoga has been divorced from its roots in the ancient conceptualization of yoga to represent a means to attain purely physical well being. While it does contribute to that, that was not its original purpose.
The yogic system was first described, and compiled, by Patanjali in his Yoga Aphorisms, which are dated to the second or third century B.C.E. These yoga sutras have been translated and discussed by many interpreters -- a good modern version being that of J.H. Woods (1914). The term "yoga" itself has two different meanings in the Sanskrit, with the most commonly accepted meaning being that of joining, or yoking (Evans Wentz, 1935). The various yoga paths are means of joining the unenlightened human being to the divine nature so that the human being can eventually escape the cycle of death and rebirth.
Hatha yoga is simply one form of yoga, and the least of the forms, not yoga itself, as is often popularly believed. Hatha yoga was developed to provide the yogis with the physical conditioning and vitality in order to maintain their strict spiritual practices. It contributed to their enlightenment by being supportive, and by working with the breath, but was not the end in itself. Limiting one's work to mastering hatha yoga was to fail at the great task of enlightenment and liberation.
There has been some attempt to include this larger understanding of yoga in popularizations that focus on the physical and emotional benefits of this system. For example, in Richard Hittleman's early popular work, he noted that yoga was not exactly exercise, but that it was designed to awaken great power within the individual as well (1969). However, he expressed the goal of hatha yoga as to achieve self realization, which may not have been well understood. He focused on providing people with access to simplified versions of the asanas, o
...