Pantheism

Pantheism is a theological theory which equates God with the Universe. Often characterized as "Nature worship", it has been equally attacked by theists as being Atheism in disguise, and by atheists as being theism in disguise. Because of this ambiguity, it has also served as a label applied to many scientists of questionable religiousity, but who clearly had a spiritual reverence for nature, such as Albert Einstein and Carl Sagan. Many east Asian religions have strong Pantheistic leanings, with Buddhism, Hinduism, and Taoism all exhibiting substantial forms. Pantheist leanings appear in even the earliest texts of Buddhism and Hinduism, but the roots of the Western form are basically Older Than Steam.

Modern variations include Panentheism (which tries to bring back some of the theism by saying God is the Universe but also exists transcendant to it, and Pandeism (which incorporates Deism to saying God has become the Universe). There are significant divisions among Pantheists, based on how they view the essential nature of the revered universe.
 * Monist Physicalist (or Naturalistic) Pantheism: Only believes in the proven or material, but reveres it; generally views the world mechanically. Represented by the World Pantheist Movement.
 * Monist Idealist Pantheism: Only believes in the mental (i.e. panpsychism) and sees consciousness as the fundamental reality; tends to give credence to mental powers.
 * Dualist Pantheism: Believes in both the physical and the spiritual, with varying bias towards either side. Perhaps the driving force behind the Universal Pantheist Society.
 * Monist Neutral Pantheism and various other offshoots reject all of the above categories, but have minuscule followings due to sheer vagueness or specificity, and have not been substantially developed.

Tropes

 * A God Am I or A God Is You are also invoked, since everyone is part of nature - but since it's everyone, no one person is elevated above the rest as a result.
 * Call Nature A God Call Nature God: One of the main criticisms against naturalistic pantheism, which is based on the belief that God is non-personal, non-sentient and in fact nothing but nature in the scientific sense.
 * They say that as if it's a bad thing. Some Pantheists specifically object to using the word God, because everyone else expects it to have the personal, sentient meaning.
 * This often leads to the confusion as to whether persons such as Einstein and Sagan, who expressed high levels of respect and wonder for nature, should be considered pantheists. As Richard Dawkins also expresses similar feelings regarding nature, it's entirely possible for one to feel about something as religious persons do about their faith without being religious.
 * According to WPM, if this is the case, the person is already a Pantheist, and simply does not acknowledge it. It is, of course, possible to treat Pantheism as religion, philosophy, or both, and there are many avowed Pantheists who are also Wiccans, Unitarian Universalists, etc.
 * Cessation of Existence: Most monist physicalist, and many other Pantheists, agree that existence as an independent consciousness ends upon death, and that all parts return to the whole, though that whole can be anything from the physical universe to an over-soul.
 * Flat Earth Atheist / Nay Theist: In an interesting twist on those tropes, an RPG campaign could involve a pantheist paladin with faith in nothing but the holiness of magic.
 * Ironically, only idealist or dualist Pantheists (a minority) would believe in the magic, until it was scientifically proven. Admittedly, in most fantasy settings that is not hard.
 * Pieces of God: Pretty much the trope namer, though the standard Pantheist will believe that the pieces are all that there ever was, and still constitute some degree of a whole
 * Pandeism claims that God destroyed itself to become our Universe (tho this may be only temporary) - Pantheism claims that the pieces are all that ever was and ever will be.
 * Take a Third Option: Splits the line between atheism and theism (and so is often accused by each of belonging to the other).
 * Or may sometimes be claimed by both sides.
 * You Mean Xmas: Some people's interpretation of the Pantheist Festival of Light, a 12-day event from December 20th to 31st - which takes up the space around Winter Solstice, Christmas (which is replaced with Yule and certain naturalistic pagan traditions, depending on believers' preference), and the New Year (okay, the last second before it).

Useful links
 * Pantheism@Everything2.com -- http://everything2.com/title/Pantheism