The soul must practice the following instructions if it wishes to attain in a short time holy recollection and spiritual silence, nakedness, and poverty of spirit, where one enjoys the peaceful comfort of the Holy Spirit, reaches union with God, is freed of all the obstacles incurred from the creatures of this world, defended against the wiles and deceits of the devil, and liberated from one’s own self.
It should be noted, then, that all the harm the soul receives is born of its enemies, mentioned above: the world, the devil, and the flesh. The world is the enemy least difficult to conquer; the devil is the hardest to understand; but the flesh is the most tenacious, and its attacks continue as long as the old self lasts.
To gain complete mastery over any of these three enemies, one must vanquish all three of them; and in the weakening of one, the other two are weakened also. When all three are overpowered, no further war remains for the soul.
Saint John of the Cross
The Precautions (excerpt)
John of the Cross, St. 1991, The Collected Works of St. John of the Cross, Revised Edition, translated from the Spanish by Kavanaugh, K and Rodriguez, O with revisions and introductions by Kavanaugh, K, ICS Publications, Washington DC.