"7. This chalice is death to the natural self, a death attained through the detachment and annihilation of that self, in order that the soul may travel by this narrow path, with respect to all its connections with sense, as we have said, and according to the spirit, as we shall now say; that is, in its understanding and in its enjoyment and in its feeling. And, as a result, not only has the soul made its renunciation as regards both sense and spirit, but it is not hindered, even by that which is spiritual, in taking the narrow way, on which there is room only for self-denial (as the Saviour explains), and the Cross, which is the staff wherewith one may reach one's goal, and whereby the road is greatly lightened and made easy. Wherefore Our Lord said through Saint Matthew: 'My yoke is easy and My burden is light'; which burden is the cross. For if a man resolve to submit himself to carrying this cross -- that is to say, if he resolve to desire in truth to meet trials and to bear them in all things for God's sake, he will find in them all great relief and sweetness wherewith he may travel upon this road, detached from all things and desiring nothing. Yet, if he desire to possess anything -- whether it come from God or from any other source -- with any feeling of attachment, he has not stripped and denied himself in all things; and thus he will be unable to walk along this narrow path or to climb upward by it."
-- St. Juan de la Cruz, The Ascent of Mount Carmel, II, xvi, 7.