The Adornment of the Spiritual Marriage, by Jan van Ruysbroeck, , at sacred-texts.com
But now you may ask me why all good men do not attain to feel this. Now listen and I will tell you the why and the wherefore. They do not respond to the stirring of God with a forsaking of themselves, and so they do not abide with quickening fervour before the Presence of God; and also they are not careful of heart in their inward self-examination. And therefore they always remain more outward and manifold than inward and simple, and they work their works more from good custom than from inward feeling. And they care more for particular methods and the greatness and multiplicity of good works than for the intention and love towards God. And so they remain outward and manifold of heart, and are not aware of how God lives in them with the fulness of grace.