There are many ancient and revered commentaries on the Bhagavad Gita, each of which has a unique emphasis. The most prominent are those of Shankara, Ramanuja, and Madhva. The most ancient commentary on the Bhagavad Gita known to the modern world is that of Shankara (CE 788-820). He refers to still earlier commentaries, but they are not available.
According to Shankara the Bhagavad Gita leads one beyond action and beyond all the distinctions of the phenomenal world to the realization of the Absolute. Shankara views the Bhagavad Gita as an expression of Advaita philosophy, and he uses the Bhagavad Gita to support his assertion that there is only one Reality without a second. His commentary emphasizes the identity of the Self with Brahman as the only Reality. In his view the phenomenal world is illusory, and taking it to be real creates bondage and suffering. Only direct knowledge of the ultimate Reality can bring freedom. Though selfless actions help to purify the mind, ultimately one goes beyond action and renounces all involvements in the mundane world...
The present commentary [Perennial Psychology of the Bhagavad Gita by Swami Rama] is unique in emphasizing the practical application of the many facets of the Bhagavad Gita's teachings. It does not exclusively emphasize action, devotion, or renunciation but delves into the way in which each of the paths and practices described in the Bhagavad Gita may be utilized to attain the Absolute.