An indulgence is "the remission before God of the temporal punishment due for sins already forgiven as far as their guilt is concerned." To obtain this remission there are proper dispositions and certain conditions predetermined by the Church that must be met by the faithful. The remission is acquired through the intervention of the Church, who has the power to loose and bind granted through Jesus Christ. "As minister of the Redemption, authoritatively dispenses and applies the treasury of the satisfaction won by Christ and the Saints"(Enchiridion of Indulgences).
To understand this practice of indulgences, the Catechism explains:
It is necessary to understand that sin has a double consequence. Grave sin deprives us of communion with God and therefore makes us incapable of eternal life, the privation of which is called the "eternal punishment" of sin. On the other hand every sin, even venial, entails an unhealthy attachment to creatures, which must be purified either here on earth, or after death in the state called Purgatory. This purification frees one from what is called the "temporal punishment" of sin. These two punishments must not be conceived of as a kind of vengeance inflicted by God from without, but as following from the very nature of sin. A conversion which proceeds from a fervent charity can attain the complete purification of the sinner in such a way that no punishment would remain.
The forgiveness of sin and restoration of communion with God entail the remission of the eternal punishment of sin, but temporal punishment of sin remains. While patiently bearing sufferings and trials of all kinds and, when the day comes, serenely facing death, the Christian must strive to accept this temporal punishment of sin as a grace. He should strive by works of mercy and charity, as well as by prayer and the various practices of penance, to put off completely the "old man" and to put on the "new man." (1472, 1473)
An indulgence can either be partial or plenary. It is partial if it removes only part of the temporal punishment due to sin, or plenary if it removes all punishment.
To be able to gain an indulgence, one must have the intention to gain them, and perform the works at the time and in the manner prescribed.
To attain a plenary indulgence, three conditions must accompany the prescribed act:
1. the faithful must receive the sacrament of confession, either eight days before or after the pious act is performed,
2. receive Holy Communion on that day
3. and recite prayers for the intentions of the Holy Father (one Our Father and one Hail Mary is the minimum, but any other additional prayers may be added).
All attachment to sin, even venial sin, must be absent. If one's disposition is less than perfect or if some of the above conditions are not fulfilled, the indulgence becomes partial.
One must also remember that one can acquire one plenary indulgence a day.
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