Perfection in an asana is achieved when the effort to perform it becomes effortless and the infinite being within is reached.

Verse 2.47

प्रयत्नशैथिल्यानन्तसमापत्तिभ्याम् ॥४७॥

prayatna-śaithilya-ananta-samāpatti-bhyām ॥47॥

Perfection in an asana is achieved when the effort to perform it becomes

effortless and the infinite being within is reached.

Verse 2.48

ततो द्वङ्द्वानभिघातः ॥४८॥

tato dvaṅdva-an-abhighātaḥ ॥48॥

From then on, the sadhaka is undisturbed by dualities

The sadhaka can be considered firm in his postures when persevering effort is no longer needed. In this stability, he grasps the physiology of each asana and penetrates within, reaching the minutest parts of the body. 

Then he gains the art of relaxation, maintaining the firmness and extension of the body and consciousness. In this way he develops a sensitive mind. 

With this sensitivity, he trains his thinking faculty to read, study and penetrate the infinite. He is immersed in the boundless state of oneness which is indivisible and universal.

 In yoga and in asana perfection must be attained through perseverance, alertness and insight. 

Without these we remain dull and make no progress Surrender to God alone does not make us perfect, although it helps us to forget the stresses of life and of our efforts, and guides us towards humility even when perfection in asana has been attained.

When the sadhaka has reached that state of balance, attention, extension, diffusion and relaxation take place simultaneously in body and intelligence, and they merge in the seat of the soul.

 This is a sign of release from the dualities of pleasure and pain, contraction and extension, heat and cold, honour and dishonour, etc.

Perfection in asana brings unalloyed happiness, blessedness and beatitude.

The effect of asana is to put an end to the dualities or differentiation between the body and mind, mind and soul. 

None of the pairs of opposites can exist for the sadhaka who is one with body, mind and soul.

When body, mind and soul unite in a perfect posture, the sadhaka is in a state of beatitude. In that exalted position, the mind, which is at the root of dualistic perception, loses its identity and ceases to disturb him. 

Unity is achieved between body and mind and mind and soul. There is no longer joy or sorrow, heat or cold, honour or dishonour, pain or pleasure. This is perfection in action and freedom in consciousness.

PATANJALI YOGA SUTRAS