Haṭha Pradīpikā Chapter One verse 17

हठस्य प्रथमाङ्गत्वाद् आसनं पूर्वम् उच्यते ।
कुर्यात् तद् आसनं स्थैर्यम् आरोग्यं चाङ्गलाघवम् ॥१७॥

haṭhasya prathama-aṅgatvād-āsanaṁ pūrvam-ucyate |
kuryāt-tad-āsanaṃ sthairyam-ārogyaṃ cāṅga-lāghvam ||

Āsana, being the initial limb of Haṭha, is spoken of first.
Āsana brings about steadiness, improved health and lightness of limb.

haṭha - force, forcefulprathamā - primary, initial, firstāsana - particular posture; sitting, sitting down; seat, place, stool; abiding, dwellingpūrva - precedingtat - that, thissthairya - steadfastness, steadinessārogya - absence of illnessca - andaṅga - limblāghava - lightness

Commentaries and Reflections

Commentary by Paul Harvey:

“For me, still to this day, one of the simplest, direct and most succinct definitions on the purpose of Āsana within the processes and practices of Haṭha Yoga, is the definition offered in the Haṭha Pradīpikā Chapter One verse 17.

It is a definition valid for any situation, discussion or presentation, or as a response to questions from any background, or level of interest around why we practice Āsana.

It can also be a springboard to linking physiological qualities, such as the relationship of Agni, to the energetic qualities of health and lightness of limb. Or investigation of the commentary by Brahmānada, as that explores psychological qualities such as the relationship of the GuṇaRajas, to mental qualities such as steadiness.”