All Orthodox Christians know from the Holy Scripture, and believe, that God created man in His own image and likeness. Therefore, in the creation man received a sinless nature, but not even the first man, Adam, remained sinless. He lost his original purity in the first fall into sin in paradise. The toxin of this sinfulness contaminated the entire human race, which descended from its forbears who had sinned - just as poison water flows from a poisoned spring. Acting upon the inclination to sin inherited from our ancestors, each person commits their own personal sins, as the Scriptural indictment says, "There is no one who will live for a single day and not sin." Only our Lord Jesus Christ is absolutely free from sin. Even the righteous, God's saints, bore sin within themselves and, although with God's help they struggled with it, yet they humbly acknowledged themselves to be sinners. So, without exception, all people are sinners, tainted with sin.
Sin is a spiritual leprosy, an illness and an ulcer which has stricken all mankind, both in his soul and his body. Sin has damaged all three of the basic abilities and powers of the soul; the mind, the heart and the will. Man's mind became darkened and inclined toward error, thus, man constantly errs - in science, in philosophy and in his practical activity.
What is even more harmed by sin is man's heart - the center of his experience of good and evil, as well as feelings of sorrow and joy. We see that our heart has been bound in the mire of sin; it has lost the ability to be pure, spiritual and Christian, to possess truly elevated feelings. Instead of this, it has become inclined toward pleasures of sensuality and earthly attachments. It is tainted with vainglory and often startles one with a complete absence of love and of the desire to do good toward one's neighbor.
What is harmed most of all, however, is the capability of our will to effect our intentions. Man proves to be without strength of will particularly when it is necessary to practice true Christian good - even though he might desire this good. The holy apostle Paul speaks of this weakness of will when he says: "For I fail to practice the good deeds I desire to do, but the evil deeds which I do not desire to do are what I am always doing." That is why Christ the Savior said of man the sinner, "Whoever practices sin is the slave of sin,"although to the sinner, alas, serving sin often seems to be freedom while struggling to escape its net appears to be slavery.
How does a sin develop in one's soul? The holy fathers, strugglers of Christian asceticism and piety, knowing the sinful human soul, explain it far better than all the learned psychiatrists. They distinguish the following stages in sin: The first moment in sin is the suggestion, when some temptation becomes identified in a person's conscience - a sinful impression, an unclean thought or some other temptation. If, in this first moment, a person decisively and at once rejects the sin, he does not sin, but defeats sin and his soul will experience progress rather than degeneration. It is in the suggestion stage of sin that it is easiest of all to remove it. If the suggestion is not rejected, it passes over first into an ill-defined striving and then into a clear, conscious desire to sin. At this point, one already begins to be inclined to sin of a given type. Even at this point, however, without an especially difficult struggle, one can avoid giving in to sin and refrain from sinning. One will be helped by the clear voice of conscience and by God's aid if one will only turn to it.
Beyond this point, one has fallen into sin. The reproaches of the conscience sound loudly and clearly, eliciting a revulsion to the sin. The former self-assurance disappears and the man is humbled (compare Apostle Peter before and after his denial of Christ). But even at this point, defeat of sin is not entirely difficult. This is shown by numerous examples, as in the lives of Peter, the holy prophet-king David and other repentant sinners.
It is more difficult to struggle with a sin when, through frequent repetition, it becomes a habit in one. After acquiring any kind of habit, the habitual actions are performed by the person very easily, almost unnoticed by himself, spontaneously. Thus, the struggle with sin which has become a habit for a person is very difficult since it is not only difficult to overcome, but is even difficult to detect in its approach and process.
An even more dangerous stage of sin is vice. In this condition, sin so rules a person that it forges his will in chains. Here, one is almost powerless to struggle against it. He is a slave to sin even though he may acknowledge its danger and, in lucid intervals, perhaps even hates it with all his soul (such is the vice of alcoholism, narcotic addiction, etc.). In this condition, one cannot deal with oneself without special mercy and help from God and one is in need of prayer and the spiritual support of others. One must bear in mind that even a seemingly minor sin such as gossiping, love of attire, empty diversions, etc. can become a vice in man if it possesses him entirely and fills his soul.
The lowest stage of sin, in which sin completely enslaves one to itself, is the passion of one or another type. In this condition, man can no longer hate his sin as he can with a vice (and this is the difference between them). Rather he submits to sin in all his experiences, actions and moods, as did Judas Iscariot. At this stage, one literally and directly lets Satan into his heart (as it is said of Judas in the Gospel) and in this condition, nothing will help him except Grace-filled Church prayers and other such actions.
There is yet another special, most terrible and destructive type of sin. This is blaspheming against the Holy Spirit. Even the prayers of the Church cannot help one who is found in this condition. The Apostle John the Theologian speaks of this directly when he entreats us to pray for a brother who has sinned, but points out the uselessness of prayer for the sin of blasphemy against the Holy Spirit.
The Lord Jesus Christ Himself says that this sin - the blasphemy against the Holy Spirit - is not forgiven and will not be forgiven either in this age or in the future. He pronounced these terrible words against the Pharisees who, though they clearly saw that he worked everything according to the will of God and by God's power, nevertheless distorted the truth. They perished in their own blasphemy and their example is instructive and urgent for all those who would sin mortal sin: by an obdurate and conscious adversity to the undoubted Truth and thereby blaspheming the Spirit of truth - God's Holy Spirit.
We must note that even blasphemy against the Lord Jesus Christ can be forgiven man (according to His own words) since it can be committed in ignorance or temporary blindness. Blasphemy against the Holy Spirit could be forgiven, says St Athanasios the Great, only if a man ceased from it and became repentant. But the very nature of the sin is such that it makes it virtually impossible for a man to return to the truth. One who is blind can regain his sight and love the one who revealed the truth to him and one who is soiled with vices and passions can be cleansed by repentance and become a confessor of the Truth, but who and what can change a blasphemer who has seen and known the Truth and who has stubbornly refused and hated it? This horrible condition is similar to the condition of the devil himself who believes in God and trembles but who nevertheless hates Him, blasphemes Him and is in adversity to Him.
When a seduction, a temptation to sin, appears in man, it usually comes from three sources: from man's own flesh, from the world and from Satan.
Concerning man's flesh, there is absolutely no doubt that in many respects it is a den and source of anti-moral predisposition's, strivings and inclinations. The ancestral sin - this inclination towards sin, a heritage from the sin of our progenitors and our own personal sinful experiences: all this added up and each (experience) strengthening one another, creates in our flesh a source of temptations, sinful moods and acts.
More often, though, the source of seduction for us is the world around us which, according to the Apostle John the Theologian, "is under the power of the Evil-One" and friendship with which, according to another Apostle, is enmity with God. The milieu around us seduces us, the people around us do likewise (especially the willful, conscious seducers and corrupters of youth about whom the Lord said: "Whoever causes one of these little ones to stumble and sin, it were better for that man that a millstone be tied around his neck and he be cast into the sea."
The enticers are also external goods, riches, comforts, immoral dances, dirty literature, shameless attire, etc. - all of this is undoubtedly a fetid source of sin and seduction.
But the main and root source of sin is, of course, the devil, as the Apostle John the Theologian says, "He who practices sin is of the devil; for the devil has sinned from the beginning." In struggling with God and His Truth, the devil struggles with people, striving to destroy each of us. He struggles most intensely and with the most malice with the saints as we see in the Gospel and in the lives of the saints. We, sick and infirm, are specially defended by Christ against those fierce temptations to which God's saints, strong in spirit, are subjected. Nevertheless, Satan does not ignore us, acting through the enticements of the world and the flesh, making them stronger and more deceptive, and also tempting us by sinful suggestions of all kinds. It is because of this, that the Apostle Peter compares Satan with a"raging lion which stalks about seeking whom he might devour."
On the Law of God, by Metropolitan Philaret (Voskresensky)
Translated by Hieromonk Varlaam Novakshonoff