St. Nicodemus the Hagiorite: Resistance to Sin

If you feel sometimes such a strong upsurging of sin that resistance to it will seem impossible and the very zeal to oppose it will appear exhausted, take care, brother, not to give up the struggle, but rouse yourself and stand firm. It is a subterfuge of the enemy, who, with the thought that resistance is hopeless, strives to undermine your firm stand and by making you lay down all your arms to force you to surrender to him. Make your mind see this subterfuge of the enemy more clearly and do not give ground. For so long as your will does not incline toward this passionate urge you are still among the victors, the fighters and slayers of the enemy, even if your sympathy is already ranged on the side of the passion. Nothing and nobody can force your will or steal victory from your hands an overthrow you against your will, no matter how obdurate and bitter the war waged in you by the enemies of your salvation. God endowed our free will with such power, that even if all a man's faculties, the whole world and all the demons rose up in arms against him and attacked him, they could not compel it. It is always left free to desire what they offer or demand, if it so wishes, or not to desire it, if it does not wish. On the other hand, for this very reason his will bears the responsibility for everything and is subject to judgment. Remember this well: no matter how weak and exhausted you may feel, you cannot find excuses for inclining toward a passionate suggestion. Your conscience will tell you the same. So the stronger the attacks the stronger the resistance you must prepare, and never abandon this resolve, repeating on all such occasions the word of command of one of our war leaders: "Watch ye, stand fast..., quit you like men, be strong" (1 Cor 16:13).
+St. Nicodemus the Hagiorite, from Unseen Warfare, chapter 14.

Note: Unseen Warfare was taken from a work originally entitled The Spiritual Combat, by the Roman Catholic scholar Lorenzo Scupoli. It was translated into Greek and edited by St. Nicodemus to conform to Orthodox teaching, and later revised by St. Theophan the Recluse who also renamed it. Thus, to some extent, each of these could be credited with the quotation.