The Book of Supreme Truth, by St. John of Rusybroeck (1293-1381)

Behold, this Eternal Love, which lives within the spirit, and with which it is united without means, gives its light and its grace to all the powers of the soul; and becomes thereby the cause of all the virtues. For the grace of God touches the highest powers of the soul, and from this touch there spring charity and the knowledge of truth, the love of all righteousness, the practice of the counsels of God according to discretion, freedom from images, the overcoming of all things without effort, and the death into the Unity through love. As long as a man can maintain himself in this exercise, he is able to contemplate, and to feel the union without means; and he feels the touch of God within himself, which is a renewal of grace and all virtues. You must further know that the grace of God also pours forth even through the lowest powers, and touches a man's heart; and from this there comes forth a heart-felt love towards God and a sensible joy in Him; and the love and delight pierce through heart and senses, through flesh and blood, and the whole bodily nature, and cause a pressure and restlessness in all his members, so that he is often at his wit's end. For he feels like a man full of wine, who is no longer master of himself. And from this there come many a strange state, wherein men of tender heart cannot well govern themselves. Sometimes through impatient longing, they lift up their heads and gaze with wide-opened eyes towards heaven; now joying, now weeping; now singing, now crying; now in weal, now in woe, and often both together; running and jumping, laughing, clapping their hands, kneeling, bowing down: and many other like gestures are seen in them. So long as a man remains thus, and lifts himself up with an open heart towards those riches of God which live in his spirit, he feels ever anew the stirring of God, and the impatience of love; and then all these things are renewed in him. And so this man through this bodily feeling may sometimes pass into a ghostly feeling which is according to reason; and through this ghostly feeling, he may pass into a godly feeling, which is above reason; and, through this godly feeling, he may drown himself in an unchangeable and beatific feeling. This feeling is our superessential blessedness, which is a fruition of God and all His beloved: and this blessedness is that Dark Quiet which ever abides in idleness. To God it is essential, and to all creatures superessential. And there we may behold how the Persons give place and abide in the Essential Love, that is, in the Fruitive Unity and yet they dwell for ever, according to Their personal nature, in the working of the Trinity.

- Chapter 9: Of the inward working of God's grace.