We must vigilantly guard our heart from unfitting thoughts and impressions, according to the word of the writer of Proverbs: ‘Keep thine heart with the utmost care; for out of these are the issues of life,’ (Proverbs 4:23).
To wage war only with the sins that make their appearance as actual deeds would be just as unsuccessful as cutting down weeds in a garden instead of digging them up at the root and throwing them out. Sins appear as inevitable outgrowths from their roots, the passions of the soul.
It is more serious to lose hope than to sin. The traitor Judas was a defeatist, inexperienced in spiritual warfare; as a result he was reduced to despair by the enemy's onslaught, and he went and hanged himself. Peter, on the other hand, was a firm rock: although brought down by a terrible fall, yet because of his experience in spiritual warfare he was not broken by despair, but leaping up he shed bitter tears from a contrite and humiliated heart. And as soon as our enemy saw them, he recoiled as if his eyes had been burnt by searing flames, and he took flight...
When the Spirit of God comes down to man and overflows him with the fullness of His inspiration, then the human soul overflows with unspeakable joy, for the spirit of God fills with joy whatever He touches.
No Christian believing rightly in God should ever be off his guard. He should always be on the look-out for temptation, so that when it comes he will not be surprised or disturbed, but will gladly endure the toil and affliction it causes, and so will understand what he is saying when he chants with the prophet: 'Prove me, O Lord, and try me' (Ps. 26:2 LXX). For the prophet did not say, 'Thy correction has destroyed me,' but, 'it has upheld me to the end' (Ps. 18:35 LXX).
The old man was asked, 'What is the good of the fasts and watchings which a man imposes on himself?' and he replied, 'They make the soul humble. For it is written, Consider my affliction and my trouble, and forgive all my sins' (Psalm 25:18). 'So if the soul gives itself all this hardship, God will have mercy on it.' The old man was (also) asked, 'What should a man do in all the temptations and evil thoughts that come upon him?' The old man said to him, 'He should weep and implore the goodness of God to come to his aid, and he will obtain peace if he prays with discernment. For it is written, 'With the Lord on my side I do not fear. What can man do to me?' (Psalm 118:6).
In patience is the assembly of all the virtues by which our souls are saved, as St. Ephraim says: He who acquires patience touches on every virtue; for he rejoices in sorrows, is well tested in misfortunes, is glad in perils, is ready for obedience, is filled with love, gives praise when provoked, is humble when reproached, is unwavering in misfortunes.
Even a pious person is not immune to spiritual sickness if he does not have a wise guide -- either a living person or a spiritual writer. This sickness is called prelest, or spiritual delusion, imagining oneself to be near to God and to the realm of the divine and supernatural. Even zealous ascetics in monasteries are sometimes subject to this delusion, but of course, laymen who are zealous in external struggles (podvigi) undergo it much more frequently. Surpassing their acquaintances in struggles of prayer and fasting, they imagine that they are seers of divine visions, or at least of dreams inspired by grace. In every event of their lives, they see special intentional directions from God or their guardian angel. And then they start imagining that they are God's elect, and often try to foretell the future. The Holy Fathers armed themselves against nothing so fiercely as against this sickness -- prelest.
Suppose you have ordered yourself not to eat fish; you will find that the enemy continually makes you long to eat it. You are filled with an uncontrollable desire for the thing that is forbidden. In this way you can see how Adam's fall typifies what happens to all of us. Because he was told not to eat from a particular tree, he felt irresistibly attracted to the one thing that was forbidden him.
Having filled himself with pride, the Antichrist will begin to set himself up and glorify himself as God, belching forth slander against Christ. He will do this so openly that he will command that all those who do not want to serve him as God be killed.
A haughty person is not aware of his faults, or a humble person of his good qualities. An evil ignorance blinds the first, an ignorance pleasing to God blinds the second.
God's all-saving will consists in doing good solely to acquire the Holy Spirit, as an eternal, inexhaustible treasure which cannot be rightly valued... This is the oil in the lamps of the wise virgins which could burn long and brightly, and these virgins with their burning lamps were able to meet the Bridegroom Who came at midnight, and could enter the bridechamber of joy with Him. But the foolish ones, though they went to market to buy some oil when they saw their lamps going out, were unable to return in time, for the door was already shut. The market is our life; the door of the bridechamber which was shut and which barred the way to the Bridegroom is human death; the wise and foolish virgins are Christian souls; the oil is not good deeds but the grace of the All-Holy Spirit of God which is obtained through them and which changes souls from one state to another - that is, from corruption to incorruption, from spiritual death to spiritual life, from darkness to light, from the stable of our being (where the passions are tied up like dumb animals and wild beasts) into a temple of the Divinity, into the shining bridechamber of eternal joy in Christ Jesus our Lord, the Creator and Redeemer and eternal Bridegroom of our souls.
Fire makes iron impossible to touch, and likewise frequent prayer renders the intellect more forceful in its warfare with the enemy. That is why the demons strive with all their strength to make us slothful in attentiveness to prayer, for they know that prayer is the intellect's invincible weapon against them.