Roman Catholicism teaches that there are two types of sin, mortal and venial. As described in the Catechism: “Mortal sin destroys charity in the heart of man by a grave violation of God's law; it turns man away from God, who is his ultimate end and his beatitude, by preferring an inferior good to him. Venial sin allows charity to subsist, even though it offends and wounds it.” (Para. 1855)
James McCarthy sums up the teaching thus (bracketed numbers are paragraphs in the Catechism): “Roman Catholic theologians compare the manner in which mortal and venial sins affect the soul to the way in which illnesses affect the body. Most ailments are minor. The body’s immune system fights them off and eventually restores health. A venial sin is like a minor sickness of the soul. It hinders spirituality and lowers resistance to temptation, but the vitality of the soul survives . Mortal sin is a deathblow. It kills the soul as surely as a fatal disease kills the body. When a Catholic who has received sanctifying grace through baptism commit’s a mortal sin, he loses that grace . Though by baptism he had been justified, because of mortal sin he forfeits the grace of justification, or, it might be said, is dejustified. He becomes a child of wrath and destined for hell [1033, 1861, 1874]. And just as a dead body has no capacity to restore itself, the Church teaches that a soul struck dead by mortal sin cannot revive itself. The sinner must turn to the Church and to the sacrament of penance [1446, 1856].” (The Gospel According to Rome, pp.75,76)
Biblically-speaking, all sin is mortal in that all sin not forgiven through faith in Christ condemns one to eternal separation from God. While under Catholic teaching one is required to confess mortal sins to a priest, who will prescribe a work of penance for forgiveness and release from eternity in Hell, Scripture says we confess our sins directly to God for forgiveness (1 John 1:8-9; Heb. 4:16, 1 John 2: 1,2) and our salvation has never been in danger.
Purgatory: Invented by Pope Gregory the Great in 593, this didn’t become dogma until 1439 because of so much reluctance to accept such an unbiblical idea. Catholicism teaches that Christ’s death made it possible to be forgiven of sin, but the sinner must still undergo some pain and torment in order to be purged and made acceptable to enter heaven. This “purging” is of unknown intensity and duration. “While Catholicism says it is theoretically possible to be cleansed through the sufferings of this life and one’s death, no one, not even the pope himself, can know whether that has occurred. Consequently, almost all Catholics expect to spend some unknown length of time in purgatory.” (Dave Hunt, A Woman Rides the Beast, p.475)
The Second Ecumenical Council of the Vatican, which was held from 1962 to 1965, stated this about purgatory: “The doctrine of purgatory clearly demonstrates that even when the guilt of sin has been taken away, punishment for it or the consequences of it may remain to be expiated or cleansed. … [I]n purgatory the souls of those who died in the charity of God and truly repentant but who had not made satisfaction with adequate penance for their sins and omissions are cleansed after death with punishments designed to purge away their debt.”
Paragraphs 1030-1032 of the Catechism say, “All who die in God's grace and friendship, but still imperfectly purified, are indeed assured of their eternal salvation; but after death they undergo purification, so as to achieve the holiness necessary to enter the joy of heaven. The Church gives the name Purgatory to this final purification of the elect, which is entirely different from the punishment of the damned. The Church formulated her doctrine of faith on Purgatory especially at the Councils of Florence and Trent. The tradition of the Church, by reference to certain texts of Scripture, speaks of a cleansing fire: ‘As for certain lesser faults, we must believe that, before the Final Judgment, there is a purifying fire. He who is truth says that whoever utters blasphemy against the Holy Spirit will be pardoned neither in this age nor in the age to come. From this sentence we understand that certain offenses can be forgiven in this age, but certain others in the age to come.’ This teaching is also based on the practice of prayer for the dead, already mentioned in Sacred Scripture: ‘Therefore [Judas Maccabeus] made atonement for the dead, that they might be delivered from their sin.’… The Church also commends almsgiving, indulgences, and works of penance undertaken on behalf of the dead.”
Catholics are taught that the living can help those in purgatory by saying prayers, giving alms and doing good works, which merits are then offered on the behalf of those in purgatory. Requesting a Mass on the behalf of the dead is supposedly the most effective means (usually money is provided to the priest for this service).
What does the Bible say?
[Christ] being the brightness of His glory and the express image of His person, and upholding all things by the word of His power, when He had by Himself purged our sins, sat down on the right hand of the Majesty on high. (Hebrews 1:3, NKJV)
But he that lacketh these things is blind, and cannot see afar off, and hath forgotten that he was purged from his old sins. (2 Peter 1:9, KJV)
Since Christ died to purge our sins, there is no need for a purgatory. Additionally, Scripture says that when we die, we go to be immediately with the Lord and not in a place of purging (Luke 23:43; Philippians 1:23-24; 2 Corinthians 5:8).
Indulgences: “Another way in which the living can help the dead is by acquiring special credits, called indulgences, that cancel out temporal punishment [1032 1471]” (McCarthy, p.94)
“The doctrine of indulgences arises from Catholicism’s strange and unbiblical insistence that Christ’s sufferings for our sins upon the cross at the hands of man and God could only obtain forgiveness of guilt but still left the ‘forgiven but repentant sinner’ under the obligation of suffering for his own sins either in this life or most likely in the ‘purifying flames of purgatory.’ An indulgence presumes, through the power given to the Church, to reduce the time or intensity of the suffering in purgatory by some unknown length or amount.” (Hunt, p. 522)
Catechism, Para 1471: …“‘An indulgence is a remission before God of the temporal punishment due to sins whose guilt has already been forgiven, which the faithful Christian who is duly disposed gains under certain prescribed conditions through the action of the Church which, as the minister of redemption, dispenses and applies with authority the treasury of the satisfactions of Christ and the saints.’” ‘An indulgence is partial or plenary according as it removes either part or all of the temporal punishment due to sin.’ The faithful can gain indulgences for themselves or apply them to the dead.”
Catechism, Para 1478-1479: “An indulgence is obtained through the Church who, by virtue of the power of binding and loosing granted her by Christ Jesus, intervenes in favor of individual Christians and opens for them the treasury of the merits of Christ and the saints to obtain from the Father of mercies the remission of the temporal punishments due for their sins. Thus the Church does not want simply to come to the aid of these Christians, but also to spur them to works of devotion, penance, and charity. Since the faithful departed now being purified are also members of the same communion of saints, one way we can help them is to obtain indulgences for them, so that the temporal punishments due for their sins may be remitted.”
As you can see, this doctrine says that Christ’s atonement was insufficient for the total forgiveness of sin, and that we must therefore do additional works.
Scripture tells us our sins are forgiven in Christ and that He paid the penalty for that sin. Since Christ was purged for our sin, there is no need of purgatory, and if there is no need for purgatory, then there is even less need for indulgences to pay for lessened time in purgatory.
Rome controls its members by legalistic rules which make them fear the loss of salvation and continued punishment for sin. Additionally, Rome has enriched itself over centuries by taking money from members who think they are paying to have less time served in an imaginary purgatory. These are not actions of a church of Christ, rather they are the actions of a religious organization of man.