Vedanta is the philosophy that has evolved from the teachings of the Vedas, which are a collection of ancient Indian scriptures -- the world's oldest religious writings.
According to the Vedas, ultimate reality is all-pervading, uncreated, self-luminous eternal spirit, the final cause of the universe, the power behind all tangible forces, the consciousness that animates all conscious beings. This is the central philosophy of the Vedantist, and his religion consists of meditation on this spirit and prayer for the guidance of his intellect along the path of virtue and righteousness.
From the philosophical standpoint, Vedanta is non-dualistic, and from the religious standpoint, monotheistic. The Vedanta philosophy asserts the essential non-duality of God, soul and universe, the apparent distinctions being created by names and forms which, from the standpoint of ultimate reality, do not exist. Vedanta accepts all religions as true and regards the various deities of the different faiths as diverse manifestations of the one God.
According to Vedanta, religion is experience and not mere acceptance of certain time-honored dogmas or creeds. To know God is to become like God. We may quote scripture, engage in rituals, perform social service, or pray with regularity, but unless we realize the Divine spirit in our hearts, we are still phenomenal beings, victims of the separative existence. One can experience God as tangibly 'as a fruit lying on the palm of one's hand,' which means that in this very life we can suppress our lower nature, manifest our higher nature, and become perfect. Through the experience of God, one's doubts disappear and the 'knots of the heart are cut asunder.' By ridding himself of the desires clinging to his heart, a mortal becomes immortal in this very body. That the attainment of immortality is not the prerogative of a chosen few but the birthright of all is the conviction of every follower of Vedanta.
Vedanta asserts that Truth is universal and all humankind and all existence are one. It teaches the unity of Godhead, or ultimate Reality, and accepts every faith as a valid means for its own followers to realize the Truth. The four cardinal principles of Vedanta may be summed up as follows: the non-duality of the Godhead, the divinity of the soul, the unity of existence and the harmony of religions. On these four principles the faith of the Vedantist is based.
The essential teachings of Vedanta, as stated by Swami Vivekananda is: "Each soul is potentially divine, the goal is to manifest this divinity within by controlling nature: external and internal. Do this either by work, or worship, or psychic control, or philosophy -- by one, or more, or all these -- and be free. This is the whole of religion. Doctrines, or dogmas, or rituals, or books, or temples, or forms, are but secondary details."