To act 'according to one’s strength' means to use a little less than necessary both of food, and drink, and sleep... As for food, restrain yourself when you wish to eat a little more, and in this way you will always make use of it moderately.
If you do not experience in yourself the influence of the evil spirit, you will not know and you will not value as you should the goodness shown to you by the benevolence of the Holy Spirit; not having known the spirit that destroys, you also will not know the Life-giving Spirit. Only because of contrary opposites of good and evil, of life and death, we understand one and the other... 'Glory to God, the Wise and All-Good, that He permits the spirit of evil and death to tempt us and cause us suffering. Otherwise, how could we begin to value the consolation of Grace, the consolation of the Holy Spirit, the Comforter and Life-giver!'
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.
Sometimes younger people, or those of equal station, or older ones, teach you by means of hints which you cannot endure, and you are vexed with your teachers. We must endure and listen with love to everything useful coming from anyone, whoever he may be. Our self-love conceals our faults from us, but they are more visible to others. This is why they remark them to us. Remember, that 'we are members one of another,' and are thus obliged to mutually correct each other. If you do not bear being instructed by others, and are vexed with those who teach you, it means that you are proud, and this shows that the fault of which others hint that you should correct yourself is really in you.
But where does Christ dwell? In pure hearts, hearts that are humble and contrite, there where He is not grieved by doubt or unbelief, by indifference towards Him, Who is God and Savior; there where men do not prefer the temporal sweetness of sin; where the idols of the passions have been chased out; where crude materiality is not preferred to the Kingdom of God, where Christians often turn their thoughts to the heavenly, as those created for heaven, for eternity; there where they seek God's truth, where every day and every hour they are attentive to His commandments. Here is where Christ dwells. And what does He do there? If only we knew (some, of course, do know) what He does in souls worthy of His abiding presence--what rest, comfort and joy He imparts, what paradisical bliss He gives them to experience while still on this earth.
If some Christians cannot comprehend our Orthodox faith, its Sacraments, it proves that the minds and hearts of such persons are too impure and passionate to bear its purity and brightness, just as sick eyes cannot bear the light of the sun. This heavenly treasure can only be comprehended by the hearts of those who free their minds and feelings from worldly attachments.
Love does not reflect. Love is simple. Love never mistakes. Likewise believe and trust without refection, for faith and trust are also simple; or better: God, in Whom we believe and in Whom we trust, is an incomplex Being, as He is also simply love.
Those who meditate unceasingly upon the holy and glorious name [of Jesus] in the depths of their heart can sometimes see the radiance of their own spirit-intelligence. For when the mind is profoundly concentrated on this invocation, we feel experientially how it starts burning off all the layers of dirt that normally suffocates the soul.
Reverence with all the powers of your soul all the sacraments, and say to yourself in respect to every sacrament before the celebration or the communion of it: `This is God's mystery. I myself am only the unworthy witness or partaker of it.' Otherwise our proud intellect even wishes to search out God's mystery, and, if unable to penetrate it, rejects it as not coming under the small measure of our intellect.
Do not be despondent when fighting against the incorporeal enemy, but even in the midst of your afflictions and oppression praise the Lord, Who has found you worthy to suffer for Him, by struggling against the subtlety of the serpent, and to be wounded for Him at every hour; for had you not lived piously, and endeavored to become united to God, the enemy would not have attacked and tormented you.
If you wish that God should speedily give you hearty faith in prayer, strive with all your heart to speak and to do everything in regard to other people sincerely, and never be deceitful in your dealings with them. If you are straightforward and truthful with others, then God will give you straightforwardness and sincere faith also in reference to Himself.
What is self-justification? - Self-justification is when a man denies his sin, as we see in the case of Adam, Eve, Cain and others who have sinned but, wishing to justify themselves, denied their sin.
The truth and saving properties of our holy faith are clearly revealed by the fact that not a single Sacrament, not a single faithful prayer are left fruitless in us, but they bring and manifest their power from heaven upon our souls and bodies, cleansing our sins, and giving peace to our souls in accordance with the words of our Savior: 'Come unto Me, all ye that labor and are heavy laden, and I will give you rest' (Mt. 11:28); and delivering us from spiritual afflictions and bodily sicknesses! No, we never pray in vain to the Lord, or to the most holy Virgin, or to the angels and saints, but we receive all that we ask them for, and that tends to our salvation.
Often during the day I have been a great sinner, and at night, after prayer, I have gone to rest, justified and whiter than snow by the grace of the Holy Ghost, with the deepest peace and joy in my heart! How easy it will be for the Lord to save us too in the evening of our life, at the decline of our days! O! save, save, save me, most gracious Lord; receive me in Thy heavenly Kingdom! Everything is possible to Thee.
My brother, the passions are afflictions; and so the Lord does not excommunicate us because of them, but He says: 'Call upon me in the time of affliction; and I will deliver thee, and thou shalt glorify me'. Therefore, when beset by any kind of passion, there is nothing more useful than to call upon the Name of God. All we can do, weak as we are, is to flee for refuge to the Name of Jesus. For the passions, being demons, retreat if this Name is invoked.
As water standing behind an earth dam, and finding an aperture, washes it wider and wider and filters through it, if we do not strengthen the dam, or strengthen it insufficiently, at last, with growing weakness on our part and with repeated efforts, the water gets through with greater and greater force, so that at last it becomes very difficult, and even impossible to stop it; so also with malice hidden in the heart of man: if we let it pierce through once, twice, and thrice, it will pour out more and more powerfully, & may at last break through and overflow your dam.
Truth is the foundation of everything that has been created. Let truth be also the foundation of all your works (both inward and outward), and especially the foundation of your prayers. Let all your life, all your works, all your thoughts, and all your desires be founded upon truth.