Many consider the mystical experience the pinnacle of the spiritual journey, as close as we get in this life to seeing divine reality face to face. The insights gained are never trivial, always basic to the understanding the mystic has through their belief system. This involves direct knowledge, not inferential. We may think of some of our knowledge as direct in regular consciousness, but even "direct" sense experience is not direct knowledge. We can demonstrate that it is mediated by all sorts of beliefs, conditions, etc. We are just so used to it that it seems non-inferential.
One of the problems in the theory of mysticism, though, concerns whether a mystical experience can be (or is) structured or contextualized by theology or culture. Some mystics report an experience of pure consciousness, and some quickly seem to couch any pure consciousness in cultural or theological garb. The question is, was the experience originally contextualized in that garb, or is that a later addition?
Many mystics claim "timelessness". Bucke claimed that he became "conscious that he possessed eternal life". There is a sense of the loss of the self. Boehme and Eckhart talk about the soul having nothing, willing nothing, and being nothing. Metaphors of melting, dissolving, and sinking are used. This feature is often seen in speculative mysticism, the mysticism that focusses on metaphysical issues rather than issues of personal spirituality. Of course, the distinction is somewhat artificial.
In nature mysticism, there is a sense that all things occur within any individual in nature (Boehme's seeing nature in a stone). This is often pantheistic. In introvertive mystical experiences, the mystic "peels off" the empirical ego, and reaches a state where there is no multiplicity, only unity. Reaches Kant's noumenal self.
Usually the mystical encounter leaves the mystic overwhelmed with positive feelings.
This is not unique to mystical experience; many religious experiences are said to be unexpressible. However, it does regularly come up in the case of mystical experience.
William James gives another list of characteristics, similar to the one I have already given:
Mysticism is "the attempt to realize, in thought or feeling, the immanence of the temporal in the eternal, and of the eternal in the temporal." In other words, it is seeing the timeless in life which is bound by time. Elsewhere, he says "Mysticism may be defined as the attempt to realise the presence of the living God in the soul and in nature." Very theistic version of mysticism.
Mysticism is "the type of religion which puts the emphasis on immediate awareness of relation with God, on direct and intimate consciousness of the Divine presence. It is religion in its most acute and living stage." Clearly a theistic sort of definition, loaded with metaphysical and religious assumptions.
Mysticism is "a quest for truth and reality that goes beyond merely sensory or intellectual spheres, taking on the aspect of a personal passion that must know directly ultimate reality without mediation or mind or sense."
"A different kind of consciousness from the ordinary."
Stace divides between "extrovertive" and "introvertive" mysticism, with the following characteristics:
1. The Unifying Vision: all things are one
1. The Unitary Consciousness: the One, the Void; pure consciousness