The Imitation of Christ by Thomas à Kempis
BOOK THREE: INTERNAL CONSOLATION
The Fifty-Third Chapter: God’s Grace Is Not Given to the Earthly Minded
The Voice of Christ
MY CHILD, my grace is precious. It does not allow itself to be mixed with external things or with earthly consolations. Cast away all obstacles to grace, therefore, if you wish to receive its infusion.
Seek to retire within yourself. Love to dwell alone with yourself. Seek no man’s conversation, but rather pour forth devout prayer to God that you may keep your mind contrite and your heart pure.
Consider the whole world as nothing. Prefer attendance upon God to all outward occupation, for you cannot attend upon Me and at the same time take delight in external things. You must remove yourself from acquaintances and from dear friends, and keep your mind free of all temporal consolation. Thus the blessed Apostle St. Peter begs the faithful of Christ to keep themselves as strangers and pilgrims in the world. 
What great confidence at the hour of death shall be his who is not attached to this world by any affection. But the sickly soul does not know what it is to have a heart thus separated from all things, nor does the natural man know the liberty of the spiritual man. Yet, if he truly wishes to be spiritual, he must renounce both strangers and friends, and must beware of no one more than himself.
If you completely conquer yourself, you will more easily subdue all other things. The perfect victory is to triumph over self. For he who holds himself in such subjection that sensuality obeys reason and reason obeys Me in all matters, is truly his own conqueror and master of the world.
Now, if you wish to climb to this high position you must begin like a man, and lay the ax to the root, in order to tear out and destroy any hidden unruly love of self or of earthly goods. From this vice of too much self-love comes almost every other vice that must be uprooted. And when this evil is vanquished, and brought under control, great peace and quiet will follow at once.
But because few labor to die entirely to self, or tend completely away from self, therefore they remain entangled in self, and cannot be lifted in spirit above themselves. But he who desires to walk freely with Me must mortify all his low and inordinate affections, and must not cling with selfish love or desire to any creature.
 1 Peter 2:11.