Oneness is one of the key principles of spirituality. Oneness means that the individual is already one with the Creator. There is no separation between the person and the Creator. The person is the Creator itself having a physical experience.
The philosophy of oneness or Advaita has been a key part of Hinduism. The word Advaita comes from the two words A(अ) meaning “Non” and Dvaita(द्वैता) meaning “Duality”. Advaita literally means “Non-Duality”. Duality means to think that the Creator or God and you are separate. Advaita is also known as Monism.
Advaita means that the individual and the Creator (referred to as Brahman in Hinduism) are one and the same. It is discussed in the Vedas, the Upanishadas and the Brahma Sutras. It was also discussed by Shri Krishna in the Bhagavad Gita.
However, in the later years, the philosophy of duality became more popular. The principle of dualism states that the Creator and the individual are two separate entities.
The principle of oneness was re-established by Shri Adi Shankaracharya. According to the principle of Advaita established by Shri Adi Shankaracharya, the Creator is without attributes (Nirguna/निर्गुण) and without form (Nirakaara/निराकार).
Shri Ramanujacharya established the principle of Vishishtadvaita(विशिष्टद्वैता). Vishistadvaita literally means “non-duality of Reality as characterized by attributes”. According to this philosophy, the Creator possesses all of the attributes present in the Universe and takes the form of Narayana. Narayana creates the other two members of the trinity i.e. Brahma and Shiva and then creates the entire creation.
True spirituality is beyond any particular religion. Spirituality is different from religion. The main principle of spirituality is the belief that one is a spirit and the belief in the existence of the Creator. There is only one Creator. The Creator is known by different names in different religions e.g. Vishnu, Shiva, Durga, Allah, God, Jesus, etc. Religion is a set of methods which have been set, a specific path to be followed to reach the Creator. All the religions in the world are but different paths to reach the same goal i.e. the Creator.
A spiritual person understands that he/she is a part of the Creator. A spiritual person does not differentiate between people based on religion for they understand that all religions are equal and are but different ways to reach the same Creator.
By the principle of Oneness, the spiritual person also understands that not only they are a part of the Creator, they are also a part of the entire creation- the Universe, the stars, the planets, nature, plants, animals, humans etc. According to the principle of oneness, there is no separation between anyone. All are part of the one whole.
The separation that one perceives between themselves and the others is an illusion which has been created by the Creator of all that is. This illusion is referred to as “Maya” in Hinduism. Science is slowly proving that reality is an illusion. This is more established by the branch of Physics known as Quantum Mechanics.
According to the principle of Oneness, the Creator or God does not exist outside the individual. The Creator is already inside the individual since the individual is a part of the Creator.