‘Āsana brings steadiness, health and lightness of limb.’
For me, still to this day, one of the finest, 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 Yoga Pradīpikā Chapter 1 verse 17. It is a definition valid for any situation, 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 discussing physiological qualities such as the relationship of Agni to the energetic qualities of health and lightness of limb. Or it can be a springboard to discussing psychological qualities such as the relationship of the Guṇa Rajas, to mental qualities, such as steadiness.