As per Bhagavad Gita human beings all the time experienced two I or selves existing in us. One is I of ego within. Those dominated by ego never believed in god or his system. They believed more in their personal self, their own capability.
In reality the present human form was manifested by our soul atman, the spirit existing in heart. Then how can I of ego persist in such circumstances. By indulging in Bhagavad Gita we can realize that we were primarily a spirit, a consciousness that manifested human form to work out its karma, remove dross impurities within.
The real I is I of our true inner self existing in our heart as soul atman. The whole purpose of spirituality is recognizing the true inner self, believing that we are a soul atman and not the manifest physical human form.
Once we realize we are a spirit manifesting human form then we can sincerely indulge in spirituality detailed in Bhagavad Gita to reach cosmic end of life, become a pure soul atman. Indulging in religious practices (rituals) we could never realize our true identity as a soul atman.
The reason for indulging in pranayama is reaching the true self existing in heart. Through the breathing process we could reach the source existing in heart that requires pure oxygen.
I in Bhagavad Gita stand for spirit, consciousness our soul atman existing in heart.