Actual or Personal sin is every sin which we ourselves commit.

Actual sin is any wilful thought, word, or deed, or voluntary omission which violates the law of God, and is therefore an offence against God.

Actual or personal sin is of two kinds, either mortal or venial. St. John (I Epistle 5; 16) speaks of "a sin which is not to death;" this is what we call venial; and "a sin unto death;" this is what we call mortal.

Mortal sin is a thorough violation or breaking of a commandment of God, with full knowledge and deliberation. It is a turning away from God, who should be the supreme object of our love, and a turning to a created object instead. It is a grievous offence against God, by which we lose His friendship and His grace, which results in the death of the soul. (The soul lost is the death of the body, God lost is the death of the soul. St.Augustine) On this account it is called mortal -- that is, deadly -- sin.

Venial sin is either a slight infringement of the law, or it may be in some cases a great violation of the law, but rendered slight in the person who commits it through his want of sufficient knowledge, deliberation or freedom.

Venial sin is not a complete breaking of a commandment, but a tendency towards breaking it. It is not a downright turning of one's back to God, but a turning aside or slackening of our tendency to Him as the supreme object of our desires or last end. It is not abandoning God for a creature, but it is, in some degree, dallying with created objects, whilst still adhering to God. It is a sin which, though heinous in itself, does not so grievously offend God as mortal sin does.

Venial sin, although an offence against God, does not cause the forfeiture of God's friendship, nor the loss of justifying grace, as mortal sin does, but it diminishes God's love towards us, and checks the flow of His choicest gifts and actual graces. In short, it does not inflict, like mortal sin, death on the soul, but a wound. Venial sin causes a stain and a guilt in the soul, of which we can easily obtain pardon; and therefore it is in that sense called venial, from the Latin venia, pardon.

Mortal sin is the greatest of evils. It is in itself so hideous and detestable, that even were there no hell to punish it, it ought to be shunned on account of its own innate foulness.

The grievousness of an offence is measured by the dignity of the person offended, and by the claims which that person has upon our love and service. Applying this principle, it follows that mortal sin, which is a grievous offence against God, who is infinitely exalted above the highest of His creatures, and whose claim to our love infinitely surpasses all other claims, is an offence incomparable greater than an offence against any creature, and implies an infinite malice. Sin, moreover, is most opposed to God.

     God is goodness itself          Mortal Sin is absence of all good.

     God is essential order          Mortal Sin is thorough disorder.

     God is the supreme good         Mortal Sin is utter evil and corruption.

     God is essential beauty         Mortal Sin is monstrous deformity. 

     God is diffusive love           Mortal Sin is narrow, mean, selfishness.

     God is essential wisdom         Mortal Sin is blind madness. 

     God is justice and holiness     Mortal Sin is injustice and wickedness.

     God is everlasting life         Mortal Sin is everlasting death. 

     God is unfading glory           Mortal Sin is endless shame. 

Sin is a desertion, an abandonment of God: "Know thou, and see that it is an evil and a bitter thing for thee to have left the Lord thy God." (Jeremias 2; 19) And Moses says to the sinner: "Thou hast forsaken the God that begot thee and hast forgotten the Lord that created thee." (Deuteronomy 32; 48)

Mortal sin is a horrible disorder. It is placing one's good in a created object, instead of fixing it in God, who is an ocean of all goodness, beauty, happiness, and glory.

Mortal sin is a dethroning of God from one's heart. It banishes God from the soul. Isaias 59;2 says: "Your iniquities have divided between you and your God."

Mortal sin is an act of insubordination, a revolt, an open rebellion against God, who declares: "Thou hast broken My yoke, thou hast burst My hands, and thou saidst: I will not serve." (Jeremias 2;20)

It is a base contempt of God, of His authority, majesty, and friendship. It is preferring the slavery of the devil to the glorious service of God. "He that committeth sin," says St. John, "Is of the devil." (1John 3;8)

It is a daring insult which man, who is "dust and ashes," offers to a being who is infinitely great, infinitely powerful, infinitely wise, infinitely good, and infinitely holy.

It is in reality preferring misery to bliss; hell to heaven; Satan to God. "To whom have you likened Me?" says the Lord in the book of Isaias: to a base passion at which you blush, to a little pleasure that passed so quickly, to a little gold which has melted in your hands. "Be astonished, O ye heavens, at this . . . For My people have done two evils. They have forsaken Me, the fountain of living water, and have digged to themselves cisterns, broken cisterns, that can hold no water." (Jeremias 2; 12-13)

Mortal sin causes a man to forfeit the friendship of God.

It changes God from a friend into an enemy.

It destroys the beauty of the soul, and covers it with a loathsome, deadly leprosy.

It so degrades and debases man as to lead him to seek happiness in muddy waters, in feeding on husks fit only for the swine. "How exceeding base art thou become going the same way over again!" (Jeremias 2; 36)

It renders man more grovelling than the brute. We read in the Psalms, "Man, when he was in honor, did not understand; he is compared to senseless beasts, and is become like to them."

It leaves a hideous stain in the soul, deforms it, and makes it hateful in the sight of heaven. It was one single mortal sin of thought which changed thousands of bright angels into monstrous demons.

Mortal sin spreads bitterness, remorse, shame, disquietude and fear in the soul. It is a poison that tortures the conscience, and works destruction: "By what things a man sinneth, by the same also he is tormented." (Wisdom 11;17)

It destroys the value of all acquired merits: "All his justices which he had done shall not be remembered."(Ezechiel 18; 24)

It deprives the soul of all power of meriting. So long as any one remains in a state of mortal sin without repenting, all the good works he does are useless to obtain any reward in heaven. St. Paul writes: "If I have not charity, I am nothing." (1 Corinth. 13; 2)

It renders a man the slave of sin, and of his evil desires. (Romans 6; 16) His passions tyrannize over him. Our Lord says: "Whosoever committeth sin, is the servant of sin." (John 8; 34)

Mortal sin causes the death of the soul."All iniquity," says Ecclesiasticul, "is like a two-edged sword" with which a man attacks God, and at the same time kills his own soul. In the same book of Ecclesiasticus we read, "The teeth thereof," that is, of sin, "are the teeth of a lion killing the souls of men." And in St. James it is said: "But sin when it is completed begetteth death."

Finally, mortal sin closes the gates of heaven against us, and unless remitted before death, entails the dreadful punishment of "everlasting fire which was prepared for the devil and his angels." (Matt.25;41)

Through Thy great mercy, O God, and through the merits of Jesus Christ, forgive us our sins. From all sin, Lord Jesus, deliver us.

Source of above information concerning SIN is from "Catholic Belief" by Rev. Joseph Faa Di Bruno, D.D. Author's American Edition Edited By Rev. Louis A. Lambert 1884 with * Imprimatur 1883 -- Henricus Eduardus, and John Cadinal McCloskey, Archbishop of New York, 1884