For those who begin to take their spiritual lives seriously, it is typical to become anxious over the obstacles that may arise between ourselves and the Lord. While misdirected, this eagerness to grow in holiness can quickly become an anxious over-analyzation of each of our acts. Was that a mortal sin or a venial sin? Unfortunately, these types of questions can become obstacles in themselves to our growth in love.
Still, the work of St. Thomas in question 88. of the Summa Theologiae can put our minds at ease and guide us to further action regarding the stumbling blocks between ourselves and the Lord. With His insight, we can have some clarity regarding sin’s subjective and objective natures.
St. Thomas begins by explaining that to understand sin, we must realize our goal (ontology, teleology) in this life, as sin represents a movement that is off course from where we are meant to go. The purpose of our existence is to move eternally toward God. That said, whether a sin is venial or mortal is determined by our intent and how gravely the action in question takes us off the path to God.
“Sin… is said to be mortal by comparison with disease, which is said to be mortal, through causing an irreparable defect.” (Summa Theoligae, Q.88. A.1). The term mortal is in reference to death. When we sin mortally, Thomas says it is likened to the body having an irreparable disease that has taken the life of the person who is sick.
When we intentionally choose something so gravely distant from a life with God, we remove ourselves from our end. When we remove ourselves from God, we cut off the lifeline of our body and soul, essentially committing spiritual suicide. In more concise terms, the life of our soul is charity (love for God). When we replace God with something less than God, we expel that lifeline of charity, and our soul dies, and we can say that we have mortally sinned.
This is irreparable for us because Charity is a theological gift. The only way to be revived from the spiritual death that is the consequence of mortal sin is through the grace of repentance. We did not place charity in our souls, and we cannot replace it. “the spiritual life is the order to the last end.. if this order be corrupted.. it cannot be repaired through intrinsic principle.. but.. by God alone.” (Sum. Theo. Q.88 A.1) Yet, luckily for us, God is infinitely merciful, and when we sin, He is unceasingly flooding our souls with these graces of repentance, waiting for us to accept His invitation to rekindle our relationship.
Mortal sin in the thought of Aquinas depends on our charity. By our act, are we willfully rebelling against a life God has chosen for us? Are we choosing something over God, even if just for a moment? Most importantly, are we removing ourselves from a trajectory of happiness and fulfillment found in a life of friendship and service to God? If yes, remember your sin doesn’t define you, but God does, and His mercy is always waiting for your, “yes.”
Venial Sin.
Saint Thomas quotes Saint Ambrose, saying, “All sin is venial with penance.” This may be a bit confusing. However, it communicates the heart of what venial sin is in the thought of Saint Thomas Aquinas.
St. Thomas says that venial sin is a deviation from our end in God rather than a destruction of it. This means that venial sins are repairable through God’s mercy and that we can regain our direction toward Him through God’s mercy. When Saint Ambrose says that all sins are venial with penance, he suggests that all sins are repairable through repentance, not that if we do penance, our sins will be taken away. Christ is the only one who takes away our sins through the merits of His Humanity; however, to receive God’s mercy, we must desire it, and penance is a tangible sign of our sorrow and repentance.
One may wonder if a venial sin can become mortal or vice versa. When we ask these types of questions, we are referring to the classifications of mortal sins; for example, murder, idolatry, and fornication fall under the species of mortal sin because they are grave in matter, yet things like idle words and imperfect charity, quick judgment or other slight faults fall under the category of venial sin. However, Aquinas states that if venial sin is referred permanently to our end, it is considered mortal, meaning that if we take slight faults and make them our aim in life, this represents the destruction of our end and relationship with God.
To put mortal and venial sin in analogical terms, it would go something a bit like this. Imagine two friends, friend A and friend B. Friend A desires, the other friend’s wife. He knows that if he were to engage in adultery, it would destroy the relationship between him and his friend. Still, he values sex with his friend’s wife over his relationship. He goes through with it and, therefore, destroys the friendship. This would most accurately fit mortal sin. Yet, imagine that the friend is very remorseful and asks for forgiveness. Friend B grants forgiveness, and the friendship is restored. This would most accurately fit venial sin; the matter remains grave, yet the mercy of the one friend and the repentance of the other makes the offense repairable.
On the other hand,  imagine if friend A has a bad habit of using foul language, and it offends friend B. Friend b approaches his friend and asks that he wouldn’t use that kind of language in front of him; friend A values his friendship more than he values the use of improper words, so he agrees not to use the words in front of friend B. This would most accurately fit venial sin.
Yet again, imagine friend A approached the other about his use of foul language and friend B completely disregards the request to change his speech, and says I won’t change for anyone. This reaction would signal that the relationship was never significant to the friend who used bad language in the first place and that, even though it wouldn’t have cost him much to change his language, that price was still too much to maintain the friendship this would accurately describe a venial sin that can become immortal sin. .
While God’s mercy is infinite and is the cause of our joy, it is essential to treat venial sin with immense caution. Laxity in our relationship with God quickly leads to severe faults. Some of the greatest scenes are quoted, saying that they would rather die than even commit the slightest venial sin because they knew that even a slight transgression was still a transgression against Almighty God, who is deserving of our full cooperation and love , Almighty God who is earning of our full cooperation and love.
DISCLAIMER: In this question of the Summa, it seems that St. Thomas uses the etymological uses of the words venial and mortal and that is how I have chosen to investigate the question. It is not my intent to say that repentance changes the intrinsic and objective qualities of mortal sin but rather that the sin becomes repairable.
