Aasana /Posture becomes stable and comfortable due to the relaxation of effort and cognitive absorption with the Infinite.
Aasana is to consciously go into and hold one posture freezing it in space and time. In order to facilitate this, one initially needs to be mindfully skillful as per Yoga quote in the Bhagavad Gita: “Yoga is skill in action” BG 2.50 to move the different limbs of the body to become the Aasana. From there one releases all tensions and relaxes all efforts, melting into the present moment, total presence. Once total stillness is achieved physically, the mind finds its own ease. The mind’s turbulence is quietened because the body is still, it has nowhere to go. From a very primeval level the survival mechanism of ‘eat or be eaten’ is quelled. From that total and complete trust and relaxation of body and mind comes the opportunity to merge with the infinite space around self. And that merging with the infinite space around self opens the way towards absorption with the Infinite Within.
If your Sadhana includes Aasana, make it a practice to hold postures consciously for longer periods of time deepening relaxation and trust as you do so. Never force as forcing is the ego going against the inherent wisdom of the body (there should not be injuries in Yoga as this shows not only a lapse in mindfulness but also going against one of the very basic principles of Yoga itself which is Ahimsa or non-harm to self or others). Once you hold a posture, release all efforts and melt into the posture’s configuration totally absorbing your consciousness into the infinite space within.
What is practiced on the mat must also be practiced off the mat. Be calmly active and actively calm in all your daily transactions with life. Know that the hand of the Divine is in all events, surrender to that One which is none other than the Eternal Witness Within.