Mystical experience is defined as being the super-sensual knowledge or feeling of oneness with a higher reality. Belief in the possibility of mystical experience constitutes mysticism, which may be identified with occultism, superstition, symbolism, fancifulness, ineffectual idealism, vagueness or sentimentality. As a sociological phenomenon, mystical religion is characterized as a regressive, imagined participation in an amorphous, collective life-stream that may be viewed as nature or race or both. Psychologically, the other-worldly nature of mystical faith is in accord with schizoid personality tendencies, and mental disorders among mystics have been noted, so that it appears that introversion, dependence, and reality-avoiding temperaments may be drawn to beliefs of this nature. With religious intolerance, mysticism might also be defined as a heresy.
The heretical Gnosticism served to caution mystics of the early Christian church against an uncritical acceptance of pagan spirituality. Quietism, condemned in 1687, was a later heresy connected with otherwise orthodox Catholic mysticism in Spain and France. Although Puritanism and Quakerism in England and America evolved a strong mysticism, other Protestant schools of thought totally condemned mysticism, casting a cloud over it in the 20th century. Hinduism in all its varieties has always been particularly predisposed to mysticism. Popular Buddhism has Nirvana as its goal; but the advent of Zen combined this with a practical approach to life. The large literature of Jewish and Taoist mysticism is available, although the extent of their practice is covered in some secrecy owing to historically avowed connections with magic.
The mystical experience is not restricted to religious experiences. They occur in a great variety of fields, in numerous ways, and with all degrees of depth and inclusiveness. Lofty appreciation of beauty or sublimity, absorbed enjoyment of music, serene companionship with nature, sudden insight into the meaning of truth, the awakening of love, moral exaltation of life in the pursuit of duty, illustrate some types of experience which immensely transcend knowledge, experiences in which the subject and object are fused into an undifferentiated one, and in which self is identified with object.
Mysticism exists as a primary characteristic in Hinduism and Buddhism. Mysticism in the 'Abrahamic' religions, Judaism, Christianity and Islam, exists as orthodox expressions of religiousity but it is closely monitored by the ecclesiastics of these faiths.
Christian mysticism recognizes a distinction between the pantheistic yearning for oneness with an impersonal All and the mystical response of faith to the life of an historical Saviour. This in effect denies all other forms of mysticism and breeds religious intolerance.
Medical research is revealing that ecstatic experience and mental illness are linked. Perhaps many of the great mystics in history were simply manic-depressives. They may not have really seen God, but merely experienced a pleasant delusion caused by their psychotic state.
Thomas Merton points out that mysticism is part of the normal Christian life, not paranormal or eccentric, not a privileged vocation for the super-pious. The ordinary Christian is either a mystic or does not exist.
Mysticism which places spiritual reality as higher than mundane reality or as true reality must be separated from the mystical experience in which the spiritual and the non-spiritual are interdependent realities. Attempts to live in one realm to the exclusion of the other leads to materialism or a perverse form of mysticism, separated from reality and ultimately self-destructive.