The priest gives us a penance after confession that we may make some atonement to God for our sins, receive help to avoid them in the future, and make some satisfaction for the temporal punishment due to them.
Perhaps it should first be observed that all penances are intrinsically inadequate in order to make true satisfaction for sin. The gravity involved in any sin far outweighs our possibility to repair the lack of love toward God. The wonder of confession is God’s generosity toward us in offering us reconciliation and restoring us to his friendship.
The Church limits itself to instructing priests to impose adequate penances corresponding to the nature of each case. The custom of imposing prayer as penance is no mere formula; rather, precisely because it is prayer, it is a sign of the renewal of grace in the soul that makes authentic prayer possible and meritorious.
In imposing a suitable penance there are several things to be taken into account.
First of all, the nature of the sin must be considered as penances seek to be remedial, and graver sins need more severe penances so as to awaken the conscience to their gravity, especially if repeated often. Sins of injustice such as stealing or calumny must also be remedied through some form of restitution of goods or good name.
Just as important, however, is the nature of the penitent as there is no automatic tariff corresponding to certain sins.
As far as possible a priest has to judge the spiritual weight of his penitent before imposing a suitable penance. This usually becomes clear through the manner of the confession itself. A person who has a strong spiritual resonance as well as a solid Catholic formation is more likely to benefit from penances such as reading Scripture, reciting psalms, or performing pious practices.
When a person has less knowledge of the faith and is not habituated to certain practices such as the rosary, Via Crucis, or fasting, it is probably better not to impose such penances as it is likely to lead to frustration.
The rule that the penance should be able to be fulfilled before leaving the church applies above all to this class of penitent. If the priest thinks that the customary Hail Marys and Our Fathers are inadequate in particular cases, then he could impose a doable but less formal penance. For example, he could tell the penitent to visit the Blessed Sacrament, or an altar dedicated to Our Lady, for a certain amount of time and, in this climate of intimacy, to give thanks for the pardon received and to ask help in overcoming a particular fault.
This last form of penance is often very beneficial to souls who have been away from confession for a long time and have been moved by a particular grace to seek the sacrament.
Sometimes the penance itself can be a source of conversion. There is an old anecdote of a priest who overheard a group of lighthearted young men making a wager in which the loser had to go to confession. With this knowledge the priest took his seat in the confessional and when the youth came to confess, the cleric imposed as a penance that the boy go before the church’s large crucifix and repeat 20 times: “You did this for me and I couldn’t care less.” At first the youth repeated it nonchalantly, and then more slowly and finally finished in tears. For this young man this confession was the beginning of a journey of conversion that eventually led to his becoming archbishop of Paris.