Bhūtakañcukī tadā vimukto bhūyaḥ patisamaḥ paraḥ
भूतकञ्चुकी तदा विमुक्तो भूयः पतिसमः परः॥ (sūtra III.42)
bhūta – the principal elements of the universe like air, fire, etc; kañcukī – as a veil; tadā – then; vimuktaḥ - liberation from mundane existence; bhūyaḥ - pre-eminence; pati – Śiva, the Supreme Lord; samaḥ - equal; paraḥ - perfect.
The yogi, who has transformed himself as the one without any desires, treats his gross body as a mere veil that covers the Self-illuminating Ātma. His body is of no importance to him. He considers his body as a vehicle for his movement. One cannot reach the destination with an unfit vehicle. For the same purpose, he sustains his body merely to keep it fit for his movements. In the beginning stages of spiritual practice, one should maintain a healthy physical body, as the most portent divine energy enters the aspirant and he needs to have a perfectly maintained physical body to withstand that energy. Yogic postures are of great help here, as otherwise, the spiritual energy will get stagnated at a point causing physical discomfort.
There is no connection between the gross body and the soul within. Gross body is made up of gross elements known as pañcabhūta-s, merely act as coverings to the Ātma. Sensory organs function through the gross body and cause impression in the mind. A yogi ensures that his mind is not afflicted with sensory impressions. This process automatically happens in a yogi, as he always stand immersed in bliss. It is also important to understand that soul in all the living beings are the same. There is no differentiation in the quality of the souls. What causes the divergence in the quality of different individuals is the manifestation of karma-s embedded in their souls.
This yogi who merely uses his physical body as his vehicle is a fully awakened person. He becomes absolutely perfect, just like Lord Śiva. Even though he is fully liberated in this birth itself, he continues to exist awaiting his physical body to fall. When his gross body ceases to exist (death), he merges with Lord Śiva. His soul gets dissolved into the infinity forever.