In 250 A.D., St. Cyprian of Carthage wrote: Adultery, fraud and manslaughter are ________________.
d. mortal sins
THE ANSWER IS D mortal sins
St. Cyprians mention of mortal sins reflect the common belief of the Early Church that there were degrees of sin.
When reading the Bible, Catholics are struck by the plain and simple teaching that some sins are worse than others. Even in the Old Testament, some sins were designated worse punishment that others. The New Testament continues this theme.
1 John 5:16:17 If any man see his brother sin a sin which is not unto death, he shall ask, and he shall give him life for them that sin not unto death. There is a sin unto death (King James Version)
Some Protestants have introduced the novel interpretation that the sin unto death in this verse refers to sin causing physical death (rather than spiritual death), but Catholics counter that the historically Christian interpretation (the interpretation passed down constantly thorough the successors of the apostles) tells us its referring to mortal sin.
The concept that one could not lose ones salvation was not introduced until the time of the Reformers, and not all the Reformers believed it either.
Quick Links on the Early Church: Church Fathers, Life of St. Augustine, St. Irenaeus (Bishop of Lyons), Clement of Rome, Clement of Alexandria, St. Ignatius of Antioch, Pelagianism, The Confessions by St. Augustine, The City of God by St. Augustine, the Martyrdom of Polycarp, Epistle to St. Polycarp, St. Basil the Great, St. Cyril of Jerusalem, St. Cyprian of Carthage, St. Jerome, St. Gregory of Nyssa, St. Barnabas, St. John Chrysostom, St. Ambrose, Eusebius, The Faith of the Early Church Fathers book, Did the Church Fathers Believe in Sola Scriptura? Foundations of Protestantism, Still Catholic