What Is Mortal Sin?

What Is Mortal Sin? June 10, 2024

Mortal sin is deadly sin. When we look at what sin is, we recognize that it is a transgression against God’s law. Sin damages relationships between people. It affects our relationship with the natural world. It affects our relationship with God negatively. Ultimately, sin leads to death as it is a rebellion against God. In Catholic moral theology, we distinguish between venial and mortal sin. While venial sin weakens our relationship to God, deadly sin kills this relationship. Mortal sin is a serious offense against God that results in extinguishing sanctifying grace within our soul. This may sound dramatic, because it is.

Mortal Sin
Mortal Sin is our greatest enemy

Facing Reality of Sin

“Reality cannot be ignored except at a price; and the longer the ignorance is persisted in, the higher and more terrible becomes the price that must be paid” (Aldous Huxley).

We tend to want to hide from the reality of sin. We talk about it in such a way that it loses its gravity. We want sin to be a remnant from a medieval way of looking at the world that has become archaic and irrelevant. Sin is, however, very real, and we ignore it to our peril.

Qualities of Mortal Sin

Within Catholic moral theology, we distinguish between mortal and venial sin. Both of these categories of sin refer to offenses against God. One type of sin injures our relationship with God, while the other is deadly, or mortal. What makes a sin mortal? There are three criteria.

For a sin to be mortal, three conditions must together be met: “Mortal sin is sin whose object is grave matter and which is also committed with full knowledge and deliberate consent.” (cf. Catechism of the Catholic Church, 1857).

Mortal Sin Requires Grave matter

For a sin to be considered mortal, it must be a serious offense against God. Murder is grave matter, as is adultery or fornication. There is a serious offense against God’s law involved in grave matter that is one of the conditions of mortal sin. The sinner is turning his or her back against God.

Full Knowledge

The person committing the sin must know that what he or she is doing is gravely sinful. Thus, when somebody has been far from the sacraments for years or even decades, they may need help to recognize the gravity of some of their actions. Many people may not realize it, but we have a grave obligation to keep Sunday holy by attending Mass.

Full Consent

It is not enough to be intellectually aware of the sinfulness of the act. We must consent to it freely and fully. We cannot be coerced into mortal sin, because if we are coerced, our will is not fully engaged.

So in order to commit mortal sin, we have to do something gravely wrong, know it, and do it willingly anyways. It is a sad reality that we do fall into this type of sin, which is proof of the reality of our free will. We can choose to oppose God, even though obviously this makes no sense.

Mortal Sin and Spiritual Life

Mortal sin sets us back in our spiritual life growth, since we kill the sanctifying grace that has been growing in our souls. We become unable to gain merit, since without sanctifying grace, even our good works do nothing to gain credit for Heaven.

When we sin mortally, we separate ourselves from God. What is the place where we suffer separation from God? Hell is the final destination if we die in such a state. Sin is serious business. So is there no hope?

God’s Redeeming Grace

The good news in the midst of such a terrible topic is that God’s grace is much greater. Through his sacrifice on the cross, Jesus gains the grace we need to be freed from sin. He takes upon himself the punishment that we deserve. He dies in our stead, and by so doing, frees us from sin and from death. To receive this grace, we have the sacrament of baptism. Baptism wipes away original sin and personal sin.

If we have the disgrace to fall into deadly sin after having received the sacrament of Baptism, the sacrament of Reconciliation allows us to go to the seat of God’s mercy and be cleansed of our new personal sin. For this reason, we should always be authentic and sincere when seeking his grace in this sacrament. Mortal sin is deadly sin. This is a sad reality. However, we can be cheered by the fact that God’s love is so great that he reaches down into the depths of despair we prepare for ourselves to rescue us and pull us out. We sin, but he saves.

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Devil, Division, and Us

About Fr. Nicholas Sheehy, LC
Fr. Nicholas Sheehy was ordained a Catholic priest in 2013 for the Legionaries of Christ. He has been involved in youth work including missions, retreats and apostolic outreach in Germany, Italy, the United States and Central America. He is passionate about the New Evangelization and formation for young adults and married couples. He is a spiritual director and retreat director, offering marriage preparation and marriage counseling through the Divine Mercy Clinic and Family Center. He is currently Executive Director and Chaplain of the Newman Center at St. Philip the Apostle Parish in Pasadena, California. You can read more about the author here.
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