The Marriam-Webster dictionary defines Pantheism as 1)  a doctrine that equates God with the forces and laws of the universe, 2)  the worship of all gods of different creeds, cults, or peoples indifferently; also :  toleration of worship of all gods (as at certain periods of the Roman empire).

 At its most general, pantheism may be understood positively as the view that God is identical with the cosmos, the view that there exists nothing which is outside of God, or else negatively as the rejection of any view that considers God as distinct from the universe. (The Stanford Encyclopedia of Philosophy) 

Wikipedia describes Pantheism as the belief that all of reality is identical with divinity, or that everything composes an all-encompassing, immanent god. Pantheists thus do not believe in a distinct personal or anthropomorphic god.

In the West, pantheism was formalized as a separate theology and philosophy based on the work of the 17th-century philosopher Baruch Spinoza (also known as Benedict Spinoza), whose book Ethics was an answer to Descartes' famous dualist theory that the body and spirit are separate. Although the term pantheism was not coined until after his death, Spinoza is regarded as its most celebrated advocate. His work, Ethics, was the major source from which Western pantheism spread.

Pantheistic concepts may date back thousands of years, and some religions in the East continue to contain pantheistic elements. 

There are a variety of definitions of pantheism. Some consider it a theological and philosophical position concerning God.

As a religious position, some describe pantheism as the polar opposite of atheism. From this standpoint, pantheism is the view that everything is part of an all-encompassing, immanent God. All forms of reality may then be considered either modes of that Being, or identical with it. Some hold that pantheism is a non-religious philosophical position. To them, pantheism is the view that the Universe (in the sense of the totality of all existence) and God are identical (implying a denial of the personality and transcendence of God).

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