The Upanisads, a work as authoritative and acceptable as both; and later on, the Upanisads, the Vedanta-Sutras and the Bhagavadgita acquired the colbctive name of "Prasthana- trayi " (the Trinity of Systems). " Prasthana-trayl " means the three principal authoritative works or pillars of the Vedic religion which systematically and scientifically expounded the two paths of Renunciation (mvrfti) and Energism (pravrtti). When once the Bhagavadgita came in this way to be included in the " Prasthana-trayl " and tha sovereignty of this "Prasthana-trayl" came to be firmly established, all religious opinions or cults which were, inconsistent with these three works or which could not find a place in them, came to be considered as inferior and unaccept- able by the followers of the Vedic religion.
When once this rule of writing sectarian ( sampradayika ) commentaries on the Prasthana-trayi supporting a particular doctrine came into vogue, different learned writers began to propound in their criticisms their own interpretations of the moral of the Gita on the authority of the commentaries pertaining to their particular doctrine and such criticisms began to gain authority in those particular sects. The commentaries or criticisms which are now available on the Gita, are more or less all of this kind, that is to say, they are written by Acaryas pertaining to diverse sects ; and on that account, although the original Bhagavadgita propounds only one theme, yet it has come to be believed that the same Gita supports all the various cults.