Wisdom From the Fathers:
St. Nicodemus of the Holy Mountain
Those Who Live in the World Must Protect Their Senses More than Those Ascetics in the Desert: You who are in the world, dear friend, must guard yourself even more than those who are in the desert. St. Basil wrote to someone living in the world the following advice: "Do not relax your efforts because you are in the world. In fact you are in need of greater efforts and more vigilance to achieve salvation. After all you have chosen to live in the midst of all the pitfalls and in the very stronghold of the sinful powers. You have before you constantly the instigations of sins and day and night all of your senses are being attacked by their evil desires." If we are overcome by the desire for food or drink, we do not experience such a strong attack. Being in a desolate place where one does not see or hear anything out of place or experience the other causes of sin, we are thus surrounded by a protective wall that helps to win our battles without wars, as St. Isaac said: "When one does not receive a sense perception, then he can have a victory without a struggle."
In other words, the monks who have removed themselves from the world are fighting behind trenches, but you are fighting an arm- to-arm combat against the enemies. The attacks are coming from all directions. And the causes of sin are all around you. While they stand afar off from the precipice, you are at its very edge. That great luminary of spiritual discretion, St. Poimen, once said: "Those who live far away from the world are like those who are far from a precipice and, whenever they are misled by the devil, before they reach the edge, they call upon God who comes to save them.
Those who live in the world, however, are like those who are near the precipice and when the devil draws them toward it, they have no time to call upon God and be saved but fall directly into the abyss." Therefore, because you are so close to this abyss, you are in immediate danger just as soon as you neglect or open one of your senses. God forbid! This is the reason why you want to use all your energy to protect your senses from coming into contact with sin. As it is impossible for a house not to be darkened by smoke entering from the outside, it is similarly impossible for a man not to let them without restraint, allowing all manner of passionate images to enter the soul. The wise St. Syngletike said, "Even when we do not want it, the thieves will enter through the senses. For how is it possible for a house not to be darkened by the smoke entering from outside through the doors and windows that have been left opened?"
From Chamberas, Peter A. (trans.), "Nicodemos of the Holy Mountain: A Handbook of Spiritual Counsel," (New York: Paulist Press, 1989), pp. 137 - 144