If you want to gain a speedy and easy victory over your enemies, brother, you must wage ceaseless and courageous war against all passion, especially and preeminently against self-love, or a foolish attachment to yourself, manifested in self-indulgence and self-pity. For it is the basis and source of all passions and cannot be tamed except by constant voluntary self-inflicted suffering and by welcoming afflictions, privations, calumnies, persecutions by the world and by men of the world. Failure to see the need of this pitiless attitude to yourself has always been, is and will be the cause of our failure to achieve spiritual victories, and of their difficulty, rarity, imperfection and insecurity.
So this spiritual warfare of ours must be constant and never ceasing, and should be conducted with alertness and courage in the soul; they can easily be attained, if you seek these gifts from God. So advance into battle without hesitation. Should you be visited by the troubling thought of the hatred and undying malice, which the enemies harbour against you, and of the innumerable hosts of the demons, think on the other hand of the infinitely greater power of God and of His love for you, as well as of the incomparably greater hosts of heavenly angels and the prayers of the saints, They all fight secretly for us and with us against our enemies, as it is written: 'The Lord will have war with Amalek from generation to generation' (Ex. xvii. 16).
So you must never be afraid, if you are troubled by a flood of thoughts, that the enemy is too strong against you, that his attacks are never ending, that the war will last for your lifetime, and that you cannot avoid incessant downfalls of all kinds. Know that our enemies, with all their wiles, are in the hands of our divine Commander, our Lord Jesus Christ, for Whose honour and glory you are waging war. Since He Himself leads you into battle, he will certainly not suffer your enemies to use violence against you and overcome you, if you do not yourself cross over to their side with your will. He will Himself fight for you and will deliver your enemies into your hands, when He wills and as He wills, as it is written: 'Thy Lord thy God walketh in the midst of thy camp, to deliver thee, and to give up thine enemies before thee' (Deut. xiii. 14).
If the Lord delays granting you full victory over your enemies and puts it off to the last day of your life, you must know that He does this for your own good; so long as you do not retreat or cease to struggle wholeheartedly. Even if you are wounded in battle do not lay down your arms and turn to flight. Keep only one thing in your mind and intention - to fight with all courage and ardour, since it is unavoidable. No man can escape this warfare, either in life or in death, and he who does not fight to overcome his passions and his enemies will inevitably be taken prisoner, either here or yonder, and delivered to death.
It is not without profit to bear in mind also the purpose for which God is pleased to leave us in this state of war. This purpose is the following. In the days of old, when God led Israel into the promised land, He did not order them to destroy all the peoples dwelling there, but left five tribes alien and hostile to Israel - first, to prove the chosen people and to see how firmly they believed in Him and faithfully kept His commandments, and secondly, to teach His people the art of warfare (Judges ii.21-23,iii.1-2). In the same way, He does not destroy all our passions at once, but leaves them in us, letting them fight against us till our very death, for just the same purpose, namely, to prove our love for Him and our obedience to His will, and to train us in spiritual warfare.
The blessed Theodorite speaks of this in greater detail. God, he says, does this for the following ends:
Thus, since we are always surrounded by so many enemies, whose hatred of us is so bitter, we can expect no peace or respite from them, no cessation or postponement of attacks, but must be ready for an onslaught at any moment and, when it comes, must immediately engage the enemy with courage. Naturally it would have been better, if we had not originally opened the doors of our being and let enemies and passions enter our heart and soul; but since they have already found their way into us, we cannot af ford to be negligent, but must arm ourselves against them to drive them out of us. They are shame less and stubborn and will not leave, unless driven out by force.
from Unseen Warfare