Mortal sins ((Latin) peccata mortalia) are in the theology of some, but not all, Christian denominations wrongful acts that condemn a person to Hell after death if unforgiven. These sins are considered "mortal" because they constitute a rupture in a person's link to God's saving grace: the person's soul becomes "dead", not merely weakened. A mortal sin does not usually mean a sin that cannot be repented; even after a mortal sin there is a chance for repentance. To Roman Catholics, repentance and a firm resolution to sin no more or to avoid occasions where one would be likely to give into sin (with at least imperfect contrition) restores the link to God's saving grace in the sacrament of penance; and restoration outside confession if the contrition is perfect. Perfect contrition rises from the love of God who has been grievously offended. There also must be a resolution to confess the sins in confession when possible.
If you see your brother or sister committing what is not a mortal sin, you will ask, and God will give life to such a one - to those whose sin is not mortal. There is sin that is mortal; I do not say you should pray about that. All wrongdoing is sin, but there is sin that is not mortal. (NRSV)
In Roman Catholic moral theology, a sin considered to be more severe or mortal is distinct from a venial sin (somewhat similar to the US secular common law distinction of classifying the severity of a crime as either a felony or a misdemeanor) and must meet all of the following conditions:
- Its subject must be a grave (or serious) matter.
- It must be committed with full knowledge, both of the sin and of the gravity of the offense; "Unintentional ignorance can diminish or even remove the imputability of a grave offense. But no one is deemed to be ignorant of the principles of the moral law, which are written in the conscience of every man. The promptings of feelings and passions can also diminish the voluntary and free character of the offense, as can external pressures or pathological disorders [mental illness]. Sin committed through malice, by deliberate choice of evil, is the gravest." Also, "Imputability and responsibility for an action can be diminished or even nullified by ignorance, inadvertence, duress, fear, habit, inordinate attachments, and other psychological or social factors."
- It must be committed with deliberate and complete consent, enough for it to have been a personal decision to commit the sin. "Mortal sin requires full knowledge and complete consent. It presupposes knowledge of the sinful character of the act, of its opposition to God's law. It also implies a consent sufficiently deliberate to be a personal choice. Feigned ignorance and hardness of heart do not diminish, but rather increase, the voluntary character of a sin."
The Catechism of the Catholic Church defines grave matter as:
1858. Grave matter is specified by the Ten Commandments, corresponding to the answer of Jesus to the rich young man: "Do not kill, Do not commit adultery, Do not steal, Do not bear false witness, Do not defraud, Honor your father and your mother." The gravity of sins is more or less great: murder is graver than theft. One must also take into account who is wronged: violence against parents is in itself graver than violence against a stranger.
This would also include worshiping other gods, and the Catechism quotes the Biblical prohibition against blasphemy. The Church itself does not provide a precise list of sins, subdivided into the mortal and venial categories. However, many sins are described as "grave sins", "grave offenses" or "gravely disordered actions" in the Catechism such as extramarital sex, divorce and masturbation.
|“||Canon 7. If anyone says that in the sacrament of penance it is not required by divine law for the remission of sins to confess each and all mortal sins which are recalled after a due and diligent examination, also secret ones and those that are a violation of the two last commandments of the Decalogue, as also the circumstances that change the nature of a sin, but that this confession is useful only to instruct and console the penitent and in olden times was observed only to impose a canonical satisfaction; or says that they who strive to confess all sins wish to leave nothing to the divine mercy to pardon; or finally, that it is not lawful to confess venial sins, let him be anathema (excommunicated).
Mortal sins are not to be confused with the seven deadly sins. The latter are not necessarily mortal sins; they are sins that lead to other sins.
Mortal sins may also be called "grave", "grievous", or "serious" sins.
Mortal sins must be specifically confessed and named along with how often they were done. It is not necessary to confess venial sins although they may be confessed. Venial sins are all sins that are not mortal. The Church encourages frequent use of the sacrament of confession even if a person has only venial sins.
Some acts cause automatic excommunication by the very deed itself e.g. renunciation of faith and religion, known as apostasy, a person who desecrates the Eucharist and "a person who procures a completed abortion". Those mortal sins are so serious that the Church through law has made them crimes, like abortion or heresy, to make their gravity realized. The Church excommunicates also so sinners come to repentance quickly when they would not otherwise. Because commission of these offenses is so serious, the Church forbids the excommunicated from receiving any sacrament (not just the Eucharist) and also severely restricts the person's participation in other Church liturgical acts and offices. A repentant excommunicated person may talk to a priest, usually in a confessional, about their excommunication to arrange for the remission. Remission cannot be denied to someone who has truly repented their actions and has also made suitable reparation for damages and scandal or at least has seriously promised according to church law. However, even if excommunicated, a Catholic who has not been juridically absolved is still, due to the irrevocable nature of baptism, a member of the Church in the sense that they are still considered members of the Catholic Church, albeit their communion with the Christ and the Church is gravely impaired. "Perpetual penalties cannot be imposed or declared by decree...." However, "the following are expiatory penalties which can affect an offender either perpetually...."
The Catholic teaching on mortal sin was called into question by some within the Church in the late 20th century after the Second Vatican Council. In response to these doubts, Pope John Paul II reaffirmed the basic teaching in his encyclical Veritatis Splendor. It is also maintained in the Catechism of the Catholic Church, which states: "Immediately after death the souls of those who die in a state of mortal sin descend into hell." However, the Catechism does not by name say a specific person is in Hell, but it does say that "...our freedom has the power to make choices for ever, with no turning back." Most significantly, the Catechism also proclaims that "There are no limits to the mercy of God...." and that "...although we can judge that an act is in itself a grave offence, we must entrust judgment of persons to the justice and mercy of God." We cannot see into their mind to know if it was deliberate or committed in full knowledge that it was a grave matter. Also, like the Parable of the Prodigal Son God forgives those who repent sincerely. Vatican II, in its Dogmatic Constitution Lumen Gentium, shows that mortal sin is still mortal sin although some people have tried to twist the writings.
Eastern Catholic churches
Eastern Catholic churches (autonomous, self-governing (in Latin, sui iuris) particular churches in full communion with the Bishop of Rome, the Pope), which derive their theology and spirituality from some of the same sources as the Eastern Orthodox and Oriental Orthodox, use the Latin Catholic distinction between mortal and venial sin, though they are not named mortal and venial. Similarly to the Eastern and Oriental Orthodox, the Eastern Catholic churches do not make a distinction between sins that are serious enough to bar one from receiving communion (and must be confessed before receiving once again) and those not sufficiently serious to do so.
The Catechism of the Catholic Church (CCC) defines these sins as grave matter:
- (This is not necessarily all of the possible grave matters.)
- Abortion (any formal cooperation in it)
- Adulation of another's grave faults if it makes one an accomplice in another's vices or grave sins, but it is not grave when it only seeks to be agreeable, to avoid evil, to meet a need, or to obtain legitimate advantages
- Cheating unless the damage inflicted is so small that one who suffers it cannot reasonably consider it significant
- Defrauding a worker of his wages
- Deliberate failure to go to mass on holy days of obligation unless excused for a serious reason (for example illness or to care for infants) or dispensed by one's own pastor
- Divorce (If civil divorce, which cannot do anything to the spiritual marriage in the eyes of God, remains the only possible way of ensuring certain legal rights, the protection of inheritance, or the care of the children it is not a sin.)
- Using drugs unless on strictly therapeutic grounds
- Endangering their own and others' safety by drunkenness or a love of speed on the road, at sea or in the air
- Envy (if to the level of wishing grave harm to another)
- Extreme anger (at the level of truly and deliberately desiring to seriously hurt or kill someone)
- False allegations
- Hatred of a neighbor to the point of deliberately desiring him or her great harm
- Sex with someone of the same gender
- Lying (the gravity is measured by "the truth it deforms, the circumstances, the intentions of the one who lies, and the harm suffered by its victims" )
- Masturbation (The gravity is measured by conditions of anxiety, force of acquired habit, and/or emotional immaturity.)
- Murder and co-operation in murder (except when done in self-defense or defense of others when there is no other way). Abortion and euthanasia as well as acceptance by human society of murderous famines without trying to fix them are included as murder. "Unintentional killing is not morally imputable. But one is not exonerated from grave offense if, without proportionate reasons, he has acted in a way that brings about someone's death, even without the intention to do so.
- Perjury and false oaths
- Prostitution "While it is always gravely sinful to engage in prostitution, the imputability of the offense can be attenuated by destitution, blackmail, or social pressure." 
- Refusing or withholding a just wage
- Rich nation's refusal to aid those which are unable to ensure the means of their development by themselves
- Scandal (deliberately causing someone to sin gravely)
- Suicide "Grave psychological disturbances, anguish, or grave fear of hardship, suffering, or torture can diminish the responsibility of the one committing suicide." We should not despair of the eternal salvation of persons who have taken their own lives. By ways known to him alone, God can provide the opportunity for salutary repentance. The Church prays for persons who have taken their own lives." 
- Taking advantage of the poor
- Terrorism that threatens, wounds and kills indiscriminately
- Unfair wagers and cheating at games unless the damage is unusually light
According to Fr. Allyne Smith, "While the Roman Catholic tradition has identified particular acts as 'mortal' sins, in the Orthodox tradition we see that only a sin for which we don't repent is 'mortal.'"
In the Orthodox Church there are no "categories" of sin as found in the Christian West. In the pre-Vatican II Catholic catechism, sins were categorized as "mortal" and "venial." In this definition, a "mortal" sin was one which would prevent someone from entering heaven unless one confessed it before death... These categories do not exist in the Orthodox Church. Sin is sin. Concerning Confession, having a list of deadly sins could, in fact, become an obstacle to genuine repentance. For example, imagine that you commit a sin. You look on the list and do not find it listed. It would be very easy to take the attitude that, since it is not on a list of deadly sins, it is not too serious. Hence, you do not feel the need to seek God's forgiveness right away. A week passes and you have completely forgotten about what you had done. You never sought God's forgiveness; as a result, you did not receive it, either. We should go to Confession when we sin—at the very least, we should ask God to forgive us daily in our personal prayers. We should not see Confession as a time to confess only those sins which may be found on a list.
Though not part of the dogma of the Orthodox Church the mortal/venial distinction is assumed by some Orthodox authors and saints as a theologoumenon. For example Saint Ignatius Brianchaninov (1807–1867), in his book A Word on Death, in a chapter entitled "Mortal sin", says:
It has been said earlier that mortal sin of an Orthodox Christian, not being cured by repentance, submits him to eternal suffering; it has also been said that the unbelievers, Muslims, and other non-orthodox, even here are the possession of hell, and are deprived of any hope of salvation, being deprived of Christ, the only means of salvation. Mortal sins for Christians are the next: heresy, schism, blasphemy, apostasy, witchery, despair, suicide, fornication, adultery, unnatural carnal sins,* incest, drunkenness, sacrilege, murder, theft, robbery, and every cruel and brutal injury. Only one of this sins—suicide—cannot be healed by repentance, and every one of them slays the soul and makes the soul incapable of eternal bliss, until he/she cleans himself/herself with due repentance. If a man falls but once in any of these sins, he dies by soul: For whosoever shall keep the whole law, and yet offend in one, he is guilty of all. For he that said, Do not commit adultery, said also, Do not kill. Now if thou commit no adultery, yet if thou kill, thou art become a transgressor of the law. (James 2:10,11)
* Under "unnatural carnal sins" the next is implied: sodomy, bestiality, masturbation, and any unnatural intercourse between married people (such as using contraceptives, consummated oral or consummated anal intercourse, etc.) as is explained in the book Ascetical Trials, also written by Saint Ignatius Brianchaninov (1807–1867).
- Near the pardonable
- Near the non-mortal
- Between the mortal and the non-mortal
- Near the mortal
Nicodemus gives the following example for the seven classes of sin. "The initial movement of anger is pardonable; near to the pardonable is for someone to say harsh words and get hot-tempered. A non-mortal sin is to swear; near the non-mortal is for someone to strike with the hand. Between the non-mortal and the mortal is to strike with a small stick; near the mortal is to strike with a large stick, or with a knife, but not in the area of the head. A mortal sin is to murder. A similar pattern applies to the other sins. Wherefore, those sins nearer to the pardonable end are penanced lighter, while those nearer to the mortal end are more severely penanced."
He also stipulates seven conditions of sin:
- Who is the doer of the sin
- What sin was committed
- Why was it committed
- In what manner was it committed
- At what time/age was it committed
- Where was it committed
- How many times was it committed
Jehovah's Witnesses recognize a special class of sin for which a Christian must formally repent in prayer to God; they term these "serious sins". Baptized Witnesses are expected to seek counsel and correction from congregation elders for even a single commission of a "serious sin"; the sinner may be formally reproved or disfellowshipped if a judicial committee considers him unrepentant.
- Venial sin
- Eternal sin
- Ancestral sin
- Original sin
- Blood atonement
- Sacrament of Reconciliation (Catholic Church)
- Seven deadly sins
- Catechism of the Catholic Church
- Veritatis Splendor
- Hardon, Fr. John (2000). Modern Catholic Dictionary. Eternal Life. ISBN 096729892X.
- Donovan (STL), Colin (2002). "Perfect Contrition".
- 1 John 5:16-17
- http://www.vatican.va/archive/ENG0015/__P6C.HTM Article 1860 of The Catechism Of The Catholic Church
- http://www.vatican.va/archive/ENG0015/__P5N.HTM Article 1735 of The Catechism Of The Catholic Church
- http://www.vatican.va/archive/ENG0015/__P6C.HTM Article 1859 of The Catechism Of The Catholic Church
- "Catechism of the Catholic Church - IntraText". Vatican.va. Retrieved 2012-03-13.
- Ex 20:7; Deut 5:11
- "("2390 The sexual act must take place exclusively within marriage. Outside of marriage it always constitutes a grave sin.")". Vatican.va. Retrieved 2012-03-13.
- "("2384 Divorce is a grave offense against the natural law.")". Vatican.va. Retrieved 2012-03-13.
- "("2352 ...masturbation is an intrinsically and gravely disordered action.")". Vatican.va. Retrieved 2012-03-13.
- "Canon 1364.1". Vatican.va. Retrieved 2012-03-13.
- "Canon 1367". Vatican.va. Retrieved 2012-03-13.
- "Canon 1398". Vatican.va. Retrieved 2012-03-13.
- "Code of Canon Law". 1983. p. Can. 1347 §2.
- "Code of Canon Law". 1983. p. Can. 1358 §1. "Remission of a censure cannot be granted unless the offender has withdrawn from contumacy according to the norm of ⇒ can. 1347, §2; it cannot be denied, however, to a person who withdraws from contumacy."
- "Canon 1342.2". Vatican.va. Retrieved 2012-03-13.
- Canon 1336
- "Catechism paragraph 1035". Vatican.va. Retrieved 2012-03-13.
- "Catechism paragraph 1861". Vatican.va. Retrieved 2012-03-13.
- "Catechism paragraph 1864". Vatican.va. Retrieved 2012-03-13.
- "DOGMATIC CONSTITUTION ON THE CHURCH - LUMEN GENTIUM - CHAPTER VII - THE ESCHATOLOGICAL NATURE OF THE PILGRIM CHURCH AND ITS UNION WITH THE CHURCH IN HEAVEN No. 48". Second Vatican Council. "Since however we know not the day nor the hour, on Our Lord's advice we must be constantly vigilant so that, having finished the course of our earthly life,(255) we may merit to enter into the marriage feast with Him and to be numbered among the blessed(256) and that we may not be ordered to go into eternal fire(257) like the wicked and slothful servant,(258) into the exterior darkness where "there will be the weeping and the gnashing of teeth".(259) For before we reign with Christ in glory, all of us will be made manifest "before the tribunal of Christ, so that each one may receive what he has won through the body, according to his works, whether good or evil"(260) and at the end of the world "they who have done good shall come forth unto resurrection of life; but those who have done evil unto resurrection of judgment"."
- "Catechism of the Catholic Church". 2000. Reference Numbers 2272, 2480, 2380, 2148, 2434, 2181, 2117, 2384 to 2386, 2290 & 2291, 2539, 2277, 2302, 2152 & 2476, 2353, 2303, 2357, 2388, 2482, 2352, 2268, 2163, 2354, 2355, 2356, 2439, 2120, 2284, 2281, 2297, 2413 & 2434, 2268, 2400, 2434.
- Catechism of the Catholic Church #2413 and 2434.
- "ref # 2181". Catechism of the Catholic Church.
- Church, Catholic. Catechism of the Catholic Church #2383.
- Compendium of the Catechism of the Catholic Church. pp. ref num 523.
- (Fr. Allyne Smith, in G. E. H. Palmer, Philip Sherrard, and Bishop Kallistos Ware, trs., Phylokalia: The Eastern Christian Spiritual Texts (Skylight Press, 2000), p. 2).
- "Sin," Orthodox Church in America website: http://www.oca.org/qa.asp?id=153&sid=3
- "Nicodemus of the Holy Mountain". OrthodoxWiki. 2011-08-25. Retrieved 2012-03-13.
- Dokos, G., Exomologetarion - A Manual of Confessions by our Righteous God-bearing Father Nikodemos the Hagiorite, 2006, Thessalonica, Uncut Mountain Press, p. 83
- Dokos, G., Exomologetarion, p. 100
- Catholic Encyclopedia entry on Sin
- Catholic Encyclopedia entry on Contrition
- Catechism of the Catholic Church from the official website of the Vatican
- The Council of Trent - Session XIV - The fourth under the Supreme Pontiff, Julius III, celebrated on November 25, 1551 - The Most Holy Sacraments Of Penance And Extreme Unction
- Excerpt from the Exomologetarion of Nicodemus the Hagiorite