Eighteenth century thinker Daniel Waterland defined pantheism as God and the universe consisting of "one and the same substance." Therefore we have direct access to God in nature: plants, birds, and animals all hold the spirit of God and are manifestations of the godhead. Human souls are also part of the universal godhead.
Like pantheism, mysticism says that human beings can have a direct, unmediated experience of God. Both theologies are alike in asserting that access to God is possible without any intermediaries, such as priests, shamans, or other kinds of holy men or women.
Mysticism is related to the Enlightenment because both systems of thought privilege the individual's direct experience of a phenomenon. The hallmark of the Enlightenment, which is often said to have begun with Descartes, is the rejection of received authority or tradition in favor of what one can know directly. Descartes, for example, said the only thing he could know directly was that he had thoughts. He said he had being because he had thoughts. He famously said: "I think, therefore, I am."
Mysticism, likewise, privileges the direct experience of God, finding this more important and vital than received tradition or studying what other people have experienced about God.