Advaita Vedanta is one of the oldest schools of Indian philosophy. It was strengthened immensely by the teachings of Shri Shankaracharya in the eight century, but its roots go to far more ancient times, right to the Vedic age.
The Vedantas or the Upanishads are a part of the Vedas, the ancient scriptures of Hinduism. There are three schools of philosophy based on the Vedantas, the Dvaita, Vishista-dvaita and A-dvaita.
Dvaita is the dualistic school of Indian philosophy. In this, God and the universe are two entirely separate realities, God has created the universe and all humans and hence humans have a lower level of existence than God.
Vishista-dvaita is the philosophy of qualified monoism. In this also, God has created the universe and all humans, but they were created out of God himself, out of His own Divine substance. Therefore, here, all humans also have a divine origin and are a part of God, though having a separate reality.
The third and most intellectually strong school is the Advaita Vedanta philosophy of monism. Here, the universe has no separate reality at all. This does not mean that the Universe does not exist, but that it has no absolute reality, its reality is of the nature of Maya, it is only relatively real, that is, its reality is ambiguous. It is only God, which here is called Brahman or the Oneness, which has true reality. For humans also, our individual consciousness has no absolute reality, our individual identity is only relatively real, and it is only the Brahman or Oneness which lies at the root of our consciousness, which is real.
The difference with Vishista-dvaita is that in Vishista-dvaita, the universe and humans also are considered to be real though a part of God, but in Advaita Vedanta philosophy, the universe and our consciousness is not considered real in itself and it is only the Oneness which lies at our base, both the base of the universe and our individual consciousness, which is real.
There is hence no question of creation or divine intervention in case of Advaita Vedanta philosophy. The Brahman or Oneness is an immanent principle only, it gives reality to the world which would not exist without it. The world has arisen from it because of the cycle of expansion and contraction through which the universe moves, and this cycle is a natural cycle which is neither willed nor controlled.
Advaita Vedanta gives a goal for our spirituality because it says that the Brahman or Oneness lies at the root of our consciousness. It then becomes possible to ‘see’ or ‘experience’ the state of Brahman by seeing into our consciousness. This is done through Yoga.
The Advaitist can follow different paths of Yoga, like Raja, Gyan, Karma or Bhakti Yoga. But the ultimate goal is always the same, to become one and merge with the Oneness of Brahman. This mystical experience is the supreme goal of the path of Advaita Vedanta philosophy.
Advaita Vedanta is an immensely strengthening and ennobling path. It says directly to us that we are right now at this moment the Truth of the universe itself. There is none higher than us who can guide us or control us. We are already the highest power possible, and we need only realize this to attain the complete freedom that we all thirst for.