HOW TO GAIN A PLENARY INDULGENCE
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. (1983 Catechism ¶ 1471)
In other words, an indulgence can take away some or all of the temporal punishment due to sin, either for ourselves or for others, as we choose. Temporal punishment is one of the consequences of sin, which does not go away even if the sinner truly repents of the sin in this life; the other is eternal punishment, which is due the unrepentant sinner. The amount of punishment due a particular sin includes all the possible consequences of the sin, not only to the sinner but to the community in the present and the future. Temporal punishment can occur in this life (penance and mortification are two examples of voluntary acts that can count to reduce temporal punishment; suffering the consequences of the sin involuntarily can count as well) or in Purgatory in the hereafter. Indulgences both partial and plenary are two other ways to reduce temporal punishment. Partial indulgences take away some of the punishment, but plenary indulgences take away all of it! Like all the best deals, there are rules. Plenary indulgences are not easy to obtain.
Plenary Indulgences can be acquired only once each day for the same work (unless one is at the moment before death, in which case the person may acquire another). Another exception is on All Souls Day — November 2 — when the faithful may gain a plenary indulgence, only for the souls in Purgatory, as often as they want.
Nov 1 - Nov 8, plenary indulgences may be gained and applied to the poor souls in Purgatory.
Notice that one might acquire additional plenary indulgences the same day as long as they are for different works.
Plenary indulgences are much more demanding than partial indulgences, for they require one to do all the following.
These are “the usual conditions” for receiving a plenary indulgence:
• have the intention of gaining the indulgence
• receive the Sacrament of Penance (within several days before or after the prescribed action of the indulgence, though the same day is best, if possible)
• Pray the Our Fathers), Hail Mary, and Gloria for the intentions of the Holy Father (within several days before or after the prescribed action of the indulgence, though the same day is best, if possible). The most recent Enchiridion prescribes at least one of each, but six each is the traditional number.
• Perform the prescribed action of the indulgence. If the prescribed action of the indulgence requires a visit to a church or oratory, one must visit devoutly and recite 1 Our Father and the Creed. This doesn’t refer to any visits to a church for Confession or the Eucharist in order to fulfill the requirements listed above; it refers to such indulgences as those granted to the faithful for visiting a church on the day of its consecration, visiting their parochial church on its titular feast day, visiting the stational churches of Rome, etc.
• Be free from all attachment to sin, including venial sin. This last is most difficult, but if it can’t be fulfilled, a partial indulgence at least will be gained.