BITE-SIZE THEOLOGY (194): Why do we inherit original sin? And what is mortal sin?

Rev José Mario O Mandía

We have explained the difference between original sin (the sin of our origins or first parents) and actual or personal sin (the sin that each one of us commits).

A question that many people ask is: why is it that we inherit the sin of our first parents? Can we not refuse it?

To answer this question, we need to understand the nature of sin. Sin is real but it is not “some thing” but rather the lack of something that we ought to have. That lack of something that we ought to have is called a “privation.” We can understand this better with an analogy: blindness is real, but it is not “some thing” but the lack of something that we ought to have – the power of sight. Blindness is the privation of sight.

Since our first parents refused God’s offer, they lost all the gifts that God had given them at the moment of their creation (cf BST 54). The loss of the greatest gift – sanctifying grace – is the sin of our first parents. Because they lost it, there was no way they could pass it on. Through their sin, they deliberately and freely deprived themselves of God’s gift of sanctifying grace, and as a consequence, we their descendants cannot enjoy that gift unless we received it in the sacrament of Baptism.


Actual sin can be classified in many ways but the most important classification is based on the seriousness or gravity of the fault. Hence, we distinguish between mortal and venial sin.

Where do we find mortal sin in the Bible? In the First Letter of St John, it says, “If any one sees his brother committing what is not a mortal sin, he will ask, and God will give him life for those whose sin is not mortal. There is sin which is mortal; I do not say that one is to pray for that. All wrongdoing is sin, but there is sin which is not mortal” (I John 5:16-17).

When is a sin mortal? The Compendium of the Catechism of the Catholic Church (no 395) explains (1) the elements or conditions that go into every mortal sin; (2) the consequences of mortal sin; and (3) the way one can obtain forgiveness of mortal sin.

ELEMENTS or CONDITIONS. One commits a mortal sin when the following are simultaneously present: (1) grave or serious matter; (2) full knowledge (the person knows what he is doing); and (3) deliberate consent (he wilfully does it).

EFFECTS. Mortal sin (1) destroys charity in us; (2) deprives us of sanctifying grace, and, (3) if unrepented, leads us to the eternal death of hell.

FORGIVENESS. It can be forgiven in the ordinary way by means of the sacraments (1) of Baptism and (2) of Penance or Reconciliation.

A person who commits just one single mortal sin excludes himself, freely and deliberately, from God’s friendship. Mortal sin is like closing the doors of the heart to anything that is from God, including God’s offer of love and eternal happiness. Sin destroys charity, and as Saint Paul says in his First Letter to the Corinthians (13:1-3), when we lack charity (love), we lack everything else because charity is at the very core of holiness.

One does not have to deliberately and explicitly say that he hates or abhors God in order to commit a grave or mortal sin. It is enough that he disobeys the commandments in some serious matter. Thus our Lord told his apostles that loving God means observing the commandments (cf John 14:15,21).

Because a person in mortal sin freely and deliberately excludes himself from God’s friendship (that is, he refuses sanctifying grace), he also excludes himself from the sacraments that require this friendship (namely, the sacraments of Confirmation, Holy Eucharist, Matrimony, Holy Orders, Anointing of the Sick). Only when he has been reconciled with God in confession may he receive these sacraments. Should he receive these sacraments knowing that he has an unconfessed mortal sin, he commits an additional mortal sin.

Mortal sin is like deliberate solitary confinement. If death comes and one has not repented, his heart is forever sealed – he will have excluded himself from enjoying infinite truth, goodness, beauty, life, and happiness.