‘Religious mysticism,’ wrote W. R. Inge in his classic Christian mysticism, ‘may be defined as the attempt to realize the presence of the living God in the soul and in nature, or, more generally, as the attempt to realize, in thought and feeling, the immanence of the temporal in the eternal, and of the eternal in the temporal.’ Many other definitions of mysticism have been formulated, and some of these have been re-examined with critical acumen by Professor R. C. Zaehner in his Mysticism sacred and profane. It is worth recalling that the mystics of Islam were equally at a loss to reach a precise and satisfactory description of the undescribable; Professor R. A. Nicholson once collected a very large list of definitions of Sufism by practising Sūfis. If mysticism in general is beyond accurate and concise definition, the particular variety of mysticism known as Sufism may perhaps be described briefly as the attempt of individual Muslims to realize in their personal experience the living presence of Allāh.

The Christian mystic in his quest for union with God relies first upon the person of Jesus Christ who, being of the Godhead, is Himself both the object of worship, the supreme model, and the goal of attainment. Next he studies the nature of God and His purpose in the world as revealed in the Holy Scriptures. For examples of mystical endeavour he turns to the lives of the saints and the writings of the mystics. Finally he seeks to prepare himself for the gift of Divine grace by observing the sacraments and acts of public worship, by the assiduous practice of self-denial, and by private meditation and other recommended forms of spiritual exercise.