Mysticism is usually thought of as being of religious in nature, which can be either monistic or theistic. The objective of monistic mysticism is to seek unity and identity with universal principles; while theistic mysticism seeks unity and oneness, but not identity with God.
Apart from religious mysticism is nonreligious mysticism, different though somewhat connected. This is more of an experiencing mysticism through, or from, the earth and nature, although some have thought to have discovered God through such experiences. An presumed authentic experience of mysticism derived from earth or nature is essentially the uniting of the subject and the object. In other words, the person becomes one with the earth and all in it; all boundaries or separation between the person and nature seem to disappear. The person becomes apart of nature, merged with it, and is not separate from it.
Instinctively every one has done what the Pagan religion openly admits to doing, and that is calling Earth, "Mother Earth." This association of Earth as a "Mother" is explained because we all are dependent on "her" for our survival. Just as a child comes to love it's mother who cares and nurtures it, so too, we love our Mother Earth who we feel loves and nurtures humankind as her children. At the very heart of the matter, this is the true definition of mysticism.
Mystical doctrines typically refer to various religious texts from different sects or cultures. Within particular religions, mystical traditions are by nature controversial, and may be considered a heretical or blasphemous belief in some cases. Most mystical teachers typically have some type of history or connection with a mainstream religion even if such belief is actually against their core religion.
The term mysticism means, in part, a stepping beyond traditional interpretation of the religion or belief and mystical traditions are often considered to be more inclusive and universalist, rejecting particular doctrines associated with traditionalist, fundamentalist, or extremist beliefs.