Before the Battle.
Before battle a warrior should act in such a way as to either repel oncoming attacks, to give himself the opportunity to notice them at the very beginning, or even to secure a victory in advance. Therefore he should first of all suppress the array of sinful movements and push them all into one place, for by doing this he will not only more easily be able to notice their rebellion, but it will be more apparent where he should direct his forces.
1) The external marks of the array of sinfulness are generally this: from its stronghold in the center of life, the heart, sin penetrates into the soul and body along all its functions, then passes through to all the person's external relationships, and finally throws its veil over everything around it. Now, although it is exiled from the depths of the heart, it still hovers through the surrounding area, feeding on what it always fed on. Faces, things and occurrences can easily arouse the same thoughts and feelings with which the person joined when he worked for sin.
The wise warrior should now guard himself from these external rations of the enemy. For this he must: a) Remodel his entire outer behavior, give a new appearance, new inspiration, new timing and so on to everything in him according the spirit of new life, b) Arrange his time so that not one hour remains without useful occupations. Breaks between duties should be taken up with something, but it should be something that facilitates the mortification of sin and strengthening of the spirit. Anyone can see just how useful certain bodily podvigs are in opposing detected tendencies, c) Bind his senses, especially the eyes, hearing and tongue, which are the most ready conductors of sin from the heart to the outside and from the outside into the heart, d) Think of spiritual substitutes for everything with which it is necessary to come into contact — things, individuals or incidents; and especially, fill his permanent living quarters with [spiritual] things that most elevate the soul, so that living thus externally, the person would live in a sort of school of Divinity. In general we should arrange our entire external environment so that in one respect it would not demand much attention, saving us much fuss over ourselves, and in another respect, that it would not only make us safe from unexpected attacks of sin, but would feed and strengthen our newly arising life in the spirit. Under such circumstances sin will be completely warded off from the outside, and will no longer receive food and support from its old source.
2) If the person now externally uses all his strength to preserve himself in his present state following his first victory, that is, if he will continually kindle those feelings and dispositions that were born in him, then sin will be warded off from the inside and will remain forever without support or substantiality. Sin thus deprived of food and support, if it is not destroyed instantly, will at least become weaker and weaker until it completely exhausts itself. After this the war with sin will obviously cease and all concentration will center on the war with thoughts (which will especially try to disrupt the new order), and rarely on passions and tendencies where it remains only to diligently watch (cf. Mk. 14:38). The warrior for Christ should have two vigilant guards — soberness and good discernment. The first is turned inward and the second is directed outward. The first watches out for movements coming from the heart itself, while the second checks the movements that can invade him from outside influences.
The rule for the first is this: after various thoughts are cast out of the heart by the remembrance of God's presence, stand by the door of the heart and diligently watch over everything that goes into it and comes out of it; especially do not allow the movement to forewarn the senses and desires, for from this comes all evil.
The rule for the second is this: at the beginning of every day, sit and go over all possible meetings and occurrences, and all the possible feelings and movements that they could cause. Fortify yourself within beforehand, so that you will not be confused and fall at some unexpected attack. By the way, in order to more successfully defend yourself at the moment of attack, it is useful to arrange an intentional preliminary mental war. Mentally place yourself in one or another situation, with this or that feeling, with one or another desire, and then invent various methods for keeping yourself within the necessary limits, and observe what particularly helped you in one or another incident. Such a preliminary exercise will develop a warring spirit, teach you to meet the enemy without timidity and to conquer it without any great difficulty, using moves learned through experience.
Furthermore, before we enter into battle we should always first find out when to act aggressively, when to act defensively and when to simply walk away. Besides the fact that we use one or another method of warfare corresponding to our degree of spiritual maturity, at first it is always best to walk away, that is, to place ourselves under God's protection without trying to fight.
Later on, when we know our enemies through experience and have studied their attacks, we can repel them without losing any time. But we should never intentionally allow them to freely arouse passions in us, or place ourselves in situations where they can work with all their might, just so that we can have an opportunity to war and gain a victory. There are particularly passionate stimuli that can only be conquered by one or another method. Thoughts should be cast out without fail; but it is not always possible to do this with tendencies and passions, especially the physical ones. In both situations the victory can be lost due to ignorance alone. Finally, never go into battle without the chief victorious thought — the sign of victory. Just as before it decided the battle between good and evil to the advantage of the former, so now does it easily make us the victors in the struggle with every sinful movement of the soul. The enemy hosts and all defiling thoughts and desires disperse at its appearance. It has the power to inspire and exalt a man above himself — therefore we must bring it to mind and to our senses as often as possible, and confirm forever in our mental stronghold this lamp that drives away the gloom. Nothing can more effectively kindle zeal for conquering sin than this thought of zeal, this rapid flood of living water, which, stirred up but not disturbed, renders unnoticeable all the waves caused by the flying stones of temptation.
During the Battle.
With these forewarnings and rules go forth to battle with good hope, O warrior of Christ. Even during battle itself you should act according to the foregoing rules, so that you do not put your hope in a disordered defense against the attacking enemy. Often one order of action, without any particular force, can crown you with success. Having noticed the enemy approach — the beginning of a stimulus, thought, passion, or tendency — first of all hasten to realize that it is the enemy. It is a great mistake, and a common one, to honor everything that comes up in us as the property of our own blood, for which we take a stand as for our own selves. Everything sinful is something foreign to us, and therefore we should always separate it from ourselves. Otherwise we will be a traitor to our own selves.
Whoever wants to war with himself should divide himself between himself and the enemy that hides in him. Having separated the known defiling movement from your own self and recognized it as the enemy, commit it then to the consciousness and senses, and engender an aversion to it in your heart. This is the most salvific means for expelling sin. Every sinful movement is held in the soul through the sensation of a certain pleasure it stimulates. Therefore, when an aversion is aroused towards it, it is deprived of all support and disappears all by itself.
This however is not always easy or even possible. It is easy to vanquish thoughts with anger, but harder to vanquish desire, and even harder to vanquish passions, for they themselves are movements of the heart. When this does not help and the enemy will not give up without a struggle, courageously enter the battle, but without self-exaltation or self-reliance. Timidity brings the soul to confusion, a certain instability and slackness, and if the soul is not sure of itself it can easily fall. Self-reliance and self-opinion are the very enemies with which we must war. Whoever has let them in has already fallen, and has even predisposed himself to new falls, because they lead a man to inactivity and blunder.
Once the struggle has begun, preserve most of all your heart: do not allow the arising movements into the feelings. Meet them at the soul's very gate and try to defeat them there. To do this you must hasten to build a conviction in your soul that is contrary to the thing on which the confusing thought hangs. Such opposing convictions are not only the shields in mental warfare but also the arrows. They defend your heart and defeat the enemy in the heart itself. From that point on the war will consist in this: approaching sin will always be guarded by thoughts and images that shield it, and the struggler will from his side destroy these strongholds by contrary thoughts and images.
The duration of the war will depend upon the multifarious circumstances, which are impossible to determine. If he does not relax a bit, or incline even intellectually towards the side of the enemy, victory will undoubtedly be his; for sinful movements, as we noted previously, do not have a firm support in us and therefore should naturally soon cease.
If after you have done all this in good conscience the enemy's defensive actions still linger in your soul like a specter and he does not want give to up his territory, then this is a sure sign that it is supported by outside help, and thus you should seek outside help, earthly or heavenly. Reveal it to your spiritual instructor and pray earnestly to the Lord, to the saints and especially to your Guardian Angel. Devotion to God has never been put to shame. You must, by the way, note another thing — war with thoughts is one thing, war with passions is another, and yet another is war with desires. Thought comes from thought, desire from desire, and passion from passion. Particular moves should be used against each one; these should be determined beforehand either by contemplation or ascetic experiences and instructions. But one should not always strictly start fighting — sometimes contempt alone expels the enemy, while fighting only multiplies and irritates him. The enemy should be followed until no traces of him are left. Otherwise, even a simple thought left in the heart like an evil snake brings forth its fruit, imperceptibly inclining the soul to itself. During the battle itself, one should not be using methods meant to prevent future battle. The rules devised for that are always very austere, and therefore it is always necessary to change them, and, it follows, admit the bankruptcy of experience inasmuch as it is harmful to spiritual warfare and tempting to the warrior.
After the Battle.
The battle is over. Thank the Lord for delivering you from defeat, but do not abandon yourself to immoderate joy of salvation, do not allow yourself to grow careless, do not slacken your zeal. The enemy often pretends to be defeated so that when you have abandoned yourself to a feeling of safety, an unexpected fall will more easily overtake you. Therefore do not put down your battle arms and do not forget your preventative rules. Always be a vigorous and vigilant warrior. Better sit and count your spoils; look over the whole process of the battle — its beginning, duration and finally what put an end to it. This will amount to a sort of tribute extracted from the loser, which will make your future victories over him exceedingly easier. This in the final analysis is how spiritual wisdom and ascetical experience are acquired.
Do not tell anyone of the victory — that would greatly irritate the enemy and make you lose your strength. Vainglory, which would be impossible to escape in this case, would open the doors of your spiritual fortress, and after gaining a victory over one enemy you would then have to do battle with a whole mob. If you are overcome, humble yourself; but do not run away from God, and do not be stubborn. Hurry to soften your heart and bring it to repentance. It is impossible not to fall, but we can and should arise after falling. When someone who runs quickly trips over something, he quickly arises and again dashes down his path to the goal. Emulate him. Our Lord is like a mother who leads her child by the hand and does not abandon him, even if he often trips and falls.
Instead of becoming paralyzed by depression, it is better to take heart for new ascetic labors, gleaning from the present fall a lesson of humility and caution not to walk in slippery places where you cannot help but fall. If you do not iron out sin with sincere repentance, then having received a degree of strength within yourself, it will inevitably draw you downward to the bottom of the sea of sin. Sin will possess you, and you will then have to start over again from the first battle. But God knows whether this will even be possible. Perhaps having committed yourself to sin, you will transgress the boundaries of conversion, and maybe you will not find afterwards even one truth that could shock your heart. Perhaps you will not even be granted the grace. Then you will already belong to the ranks of those condemned to eternal torment.
The Rules of Warfare are not the Same for All.
In general about the rules of warfare it must be noted that they are essentially nothing other than an application of all weapons to individual cases, and that is why it is impossible to describe them all. The business of inner warfare is incomprehensible and mysterious. The cases of it vary utterly, and the warring individuals are too different. What will overcome one person is indifferent to another.
Therefore it is decisively impossible to make the same set of rules for everyone. The best devisor of the rules of warfare is every individual for himself. Experience is the best teacher — one only needs to have the zealous desire to conquer himself. The first ascetics did not study from books, but nevertheless they represent the very image of conquerors. Furthermore one should not rely too much on these rules; they represent only external sketches. What makes up the essence of the matter each will know only through experience, when he begins to actually wage war. And in this work his only guides will be his own good sense and his dedication to God.
The inner path of Christian life in each individual brings to mind the ancient underground catacombs, extremely intricate and mysterious. Upon entering them, the tried one receives a few instructions on the catacomb's general features — do this here, do that there, follow a certain sign here, and another there. But then he is left alone amidst the darkness, sometimes with only the weak light of a lamp. Everything will depend upon his presence of spirit, good sense and caution, and upon invisible guidance. There is a similar mysteriousness in inner Christian life. Here each one walks alone, though he be surrounded by a multitude of rules. The promptings of the heart, and especially the hints of grace, are his only constant, undeceiving and inseparable guides in his war with himself. Everything else will abandon him.
Source: "The Path to Salvation" By Saint Theophan the Recluse