Mortal sins are the acts by which man freely rejects God
Every sin that has as its object a serious matter and that is committed with full conscience is a mortal sin, states the Catechism of the Catholic Church in paragraph 1587. Therefore, every sinful act against the 10 commandments is a serious sin. The commandments are the basis of Catholic morality. Jesus’ response to the rich young man in the Gospel of Saint Mark illustrates serious sins well: “You know the commandments: do not
You shall not commit murder, you shall not commit adultery, you shall not steal, you shall not bear false witness, you shall not harm anyone, honor your father and your mother!” (Mc 10,19)
Also watch the homily: How to be perfect in the eyes of God?
More Church Teachings on Mortal Sin
The paragraphs (§) below from the Catechism of the Catholic Church present us with a very rich teaching:
§ 1855. Mortal sin destroys charity in the heart of man by a serious infraction of the Law of God. It diverts man from God, which is his ultimate end, his blessedness, preferring Him an inferior good. Venial sin allows charity to persist, even though it offends and wounds it.
§ 1856. Mortal sin, attacking within us the vital principle that is charity, makes necessary a new initiative of God’s mercy and a conversion of heart that normally takes place within the framework of the sacrament of Reconciliation:
«When the will allows itself to be attracted by something contrary to charity, by which we are ordained for our ultimate end, sin, by its very object, must be considered mortal, whether it is against the love of God (such as blasphemy, perjury, etc.), or against the love of one’s neighbor (such as murder, adultery, etc.). On the other hand, when the sinner’s will sometimes allows itself to be led towards something that in itself is disordered, and is not However, contrary to the love of God and neighbor (such as an idle word, a superfluous risk, etc.), such sins are venial” (95).
§ 1857. For a sin to be mortal, three conditions are required at the same time: “A mortal sin is one that has as its object a grave matter, and is committed with full conscience and with deliberate purpose” (96).
§ 1861. Mortal sin is a radical possibility of human freedom, just like love itself. Its consequence is the loss of charity and the deprivation of sanctifying grace, that is, the state of grace. And if it is not rescued by repentance and God’s forgiveness, it will lead to exclusion from the Kingdom of Christ and eternal death in Hell, since our freedom has the capacity to make definitive, irreversible choices. However, although it is possible for us to judge whether an act is, in itself, a serious offense, we must entrust the judgment of people to the justice and mercy of God.
§ 1874. Deliberately opting – that is, knowingly and willingly – for something gravely contrary to divine law and the ultimate end of man, is to commit a mortal sin. This destroys charity in us, without which eternal bliss is impossible; If there is no repentance, the consequence is eternal death.
NOTE: the numbers in bold are the paragraphs generally identified in books and articles with the symbol in parentheses (§)
References:
Catholic Bible translated by CNBB