The state of oneness between the soul and the Absolute or God. The term is used more commonly among Christian mystics such as Teresa of Avila and John of the Cross. It is the highest state of spiritual perfection attainable, and is equivalent to the NIRVANA of Buddhists and FANA among the Muslim Sufis.
In mystical Christianity, mystical union is preceded by three identifiable states in the spiritual life of the aspirant. The first is the awakening where the soul feels a divine discontent that cannot be quenched by material, social or psychological objects. Then follows a period of purification, where the attachments of the soul to objects are gradually cleansed and dissipated. This is the first “dark night” of John of the Cross – the “dark night of the senses.” Among those who successfully overcome the obstacles to spiritual growth, there may come a time when the state of illumination is experienced.
It is called by various names in Christian literature, such as contemplative consciousness, spiritual consciousness, or spiritual intuition. It is during this stage where the second dark night of the soul is gone through, called “dark night of the spirit.” These may finally lead to the apex of spiritual life called mystical union. John of the Cross states that the soul’s operation “which before was human, has become Divine, which is that that is attained in the state of union, wherein the soul becomes naught else than an altar whereon God is adored in praise and love, and God alone is upon it” (Ascent to Mount Carmel, Ch. 5, Sec. 7).