How to perfect asana
Patanjali 11,47 is referring to how asana is perfected.
There is a point when persevering effort is no longer required.
By maintaining firmness (which we know comes from pranayama), extending the body extends consciousness and training the intellect to read and study to penetrate the infinite being within.
There is then an immersion into the boundless state of oneness, indivisible and universal.