There comes a time when God no longer hides his grace from us. When God knows our soul to be ready and fully mature there is a mystical union that occures.
Saint Theophan describes this state as follows: God dwells in man in a special manner. He visibly fills him, unites Himself to him and communes with him. This is the goal man strives to achieve through all the ascetic struggles and labors, all the economy of salvation from God Himself, and all that happens to each person in the present life from birth to grave. St. Macarius writes that the work of grace after long trials finally sows itself fully, and the soul acquires full sonship of the Spirit. God Himself proves the heart, and man is made worthy to become one spirit with the Lord. (Path To Salvation, p198)
According to St. Diadochos, “If a man while still alive, can undergo death through his labors, then in his entirety he becomes the dwelling-place of the Holy Spirit… Grace illumines his whole being with a deeper awareness, warming him with great love of God. (Philokalia, vol 1 no 82, 85, p 284, 285) This action reveals itself or is accompanied by different manifestations with different people.
A spiritual description by St. Macarius, The soul that is is deemed to be judged worthy to participate in the light of the Holy Spirit by becoming his throne and habitation, and is covered with the beauty of ineffable glory of the spirit, becomes all light, all face, all eye. There is no part of the soul that is not full of the spiritual eyes of light. That is to say, there is no part of the soul that is covered with darkness but is totally covered with spiritual eyes of light. FOr the sou l had no imperfect part but is in every part on all sides facing forward and covered with the beauty of the ineffable glory of the light of Christ, who mounts and rides upon the soul.” (The Fifty Spiritual Homilies, Homily 1.2, p 37)