How can I explain (including scripture references) the Church’s position on Mortal and Venial sins?
*Reconciliatio Et Paenitentia * (Reconciliation and Penance)
of Pope John Paul II to the Bishops:
On mortal and venial sin:
“The church has a teaching on this matter which she reaffirms in its essential elements, while recognizing that it is not always easy in concrete situations to define clear and exact limits.
Already in the Old Testament, individuals guilty of several kinds of sins - sins committed deliberately,(Cf Nm 15:30.) the various forms of impurity,(Cf Lv 18:26-30) idolatry,(Cf ibid., 19:4), the worship of false gods (Cf ibid., 20:1-7) - were ordered to be “taken away from the people,” which could also mean to be condemned to death.(Cf Ex 21:17) Contrasted with these were other sins especially sins committed through ignorance, that were forgiven by means of a sacrificial offering.(Cf Lv 4:2ff; 5:1ff; Nm 15:22-29).
In reference also to these texts, the church has for centuries spoken of mortal sin and venial sin. But it is above all the New Testament that sheds light on this distinction and these terms. Here there are many passages which enumerate and strongly reprove sins that are particularly deserving of condemnation.(Cf Mt 5:28; 6:23; 12:31f; 15:19; Mk 3:28-30; Rom 1:29-31; 13:13; Jas 4). There is also the confirmation of the Decalogue by Jesus himself.(Cf Mt 5:17; 15:1-10; Mk 10:19; Lk 18:20). Here I wish to give special attention to two passages that are significant and impressive.
In a text of his First Letter, St. John speaks of a sin which leads to death (pros thanaton), as opposed to a sin which does not lead to death (me pros thanaton).(Cf 1 Jn 5:16f). Obviously, the concept of death here is a spiritual death. It is a question of the loss of the true life or “eternal life,” which for John is knowledge of the Father and the Son,(Cf 1 Jn 17:3) and communion and intimacy with them. In that passage the sin that leads to death seems to be the denial of the Son (Cf 1 Jn 2:22) or the worship of false gods.(Cf 1 Jn 5:21). At any rate, by this distinction of concepts John seems to wish to emphasize the incalculable seriousness of what constitutes the very essence of sin, namely the rejection of God. This is manifested above all in apostasy and idolatry: repudiating faith in revealed truth and making certain created realities equal to God, raising them to the status of idols or false gods.(Cf 1 Jn 5:16-21). But in this passage the apostle’s intention is also to underline the certainty that comes to the Christian from the fact of having been “born of God” through the coming of the Son: The Christian possesses a power that preserves him from falling into sin; God protects him, and “the evil one does not touch him.” If he should sin through weakness or ignorance, he has confidence in being forgiven, also because he is supported by the joint prayer of the community.
In another passage of the New Testament, namely in St. Matthew’s Gospel,(Cf Mt 12:31f) Jesus himself speaks of a “blasphemy against the Holy Spirit” that " will not be forgiven" by reason of the fact that in its manifestation, it is an obstinate refusal to be converted to the love of the Father of mercies.
Moreover, Jesus’ warning about the sin “that will not be forgiven” confirms the existence of sins which can bring down on the sinner the punishment of “eternal death.”
In the light of these and other passages of sacred Scripture, doctors and theologians, spiritual teachers and pastors have divided sins into mortal and venial. St. Augustine, among others, speaks of letalia or mortifera crimina, contrasting them with venialia, levia or quotidiana. The meaning which he gives to these adjectives was to influence the successive magisterium of the church. After him, it was St. Thomas who was to formulate in the clearest possible terms the doctrine which became a constant in the church.
But when we ponder the problem of a rebellious will meeting the infinitely just God, we cannot but experience feelings of salutary “fear and trembling,” as St. Paul suggests.(92) Moreover, Jesus’ warning about the sin “that will not be forgiven” confirms the existence of sins which can bring down on the sinner the punishment of “eternal death.”
In the light of these and other passages of sacred Scripture, doctors and theologians, spiritual teachers and pastors have divided sins into mortal and venial. St. Augustine, among others, speaks of letalia or mortifera crimina, contrasting them with venialia, levia or quotidiana.(93) The meaning which he gives to these adjectives was to influence the successive magisterium of the church. After him, it was St. Thomas who was to formulate in the clearest possible terms the doctrine which became a constant in the church.
In defining and distinguishing between mortal and venial sins, St. Thomas and the theology of sin that has its source in him could not be unaware of the biblical reference and therefore of the concept of spiritual death. According to St. Thomas, in order to live spiritually man must remain in communion with the supreme principle of life, which is God, since God is the ultimate end of man’ s being and acting. Now sin is a disorder perpetrated by the human being against this life-principle. And when through sin, the soul commits a disorder that reaches the point of turning away form its ultimate end God to which it is bound by charity, then the sin is mortal; on the other hand, whenever the disorder does not reach the point of a turning away from God, the sin is venial."(94) For this reason venial sin does not deprive the sinner of sanctifying grace, friendship with God, charity and therefore eternal happiness, whereas just such a deprivation is precisely the consequence of mortal sin.
Furthermore, when sin is considered from the point of view of the punishment it merits, for St. Thomas and other doctors mortal sin is the sin which, if unforgiven, leads to eternal punishment; whereas venial sin is the sin that merits merely temporal punishment (that is, a partial punishment which can be expiated on earth or in purgatory).”
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*Mortal Sin * (The Fathers)
Catechism of the Catholic Church