The Adornment of the Spiritual Marriage, by Jan van Ruysbroeck, , at sacred-texts.com
Of this ardour there springs unity of heart; for we cannot achieve true unity unless the Spirit of God blows to a flame His fire in our hearts. For this fire makes one with itself and like to itself all that it can master and re-shape.
Unity is this: that a man feel himself to be gathered together with all his powers in the unity of his heart. Unity brings inward peace and restfulness of heart. Unity of heart is a bond which draws together body and soul, heart and senses, and all the outward and inward powers and encloses them in the union of love.