Penance can be either interior or exterior.

Interior penance consists of having sorrow for our sins with the firm purpose of not committing them, or any sin, again. This is not an intermittent sentiment but one that is constant, and it forms part of a Christian’s normal state of soul, just as sin forms part of our lives.

Exterior penance is the result of interior penance and consists of inflicting punishment on oneself for the sins that he has committed.

Exterior penance can be divided into two categories: involuntary and voluntary.

The chief type of exterior penance, if one can really call it penance, is involuntary. This consists of a filial acceptance of everything that constitutes our human condition, such as work, suffering, and death; and everything that makes us die bit by bit, such as age, sicknesses and infirmities, reverses of fortune, aches and pains, separations from and mourning of loved ones, etc. We should never forget all the consequences and punishment due to sin (“Morte morieris…”: “If you disobey me”, the Lord said to man, “you will die the death…”). Let us accept it just as it is.

To this first and chief type of involuntary penance is added exterior penance that is voluntary or freely imposed.

Exterior voluntary penance is practiced in three ways:

(1) The first method is concerned with food. When we put aside whatever is not essential in regard to eating, we practice, not penance, but rather temperance. Penance comes about when we abstain from eating what is normal for us to eat. The more we do without it, the greater is the penance; however, we must watch out that we do not compromise our health.

(2) The second method deals with sleep. Here also there is no penance when we give up what is unnecessary and what causes us to be soft and lazy. There is penance when we reduce the amount of sleep that is normal and natural to us. And, provided our health is not harmed, the more we reduce it, the better is the penance. In case one has the habit of sleeping too much, he should cut back on his normal amount of sleep for a short time in order to come to a happy mean.

(3) The third method consists of chastising the body, or in other words in inflicting physical pain on it. This is done by the use of penitential instruments: whipping cords, hairshirts, little chains made of metal. In this type of penance, it is proper to use only those instruments that cause superficial and external pain and do not result in leaving bruises. Note: It is of vital importance that a person who feels, either within the retreat or outside it, that he would like to use penitential instruments should put himself under the direction of a prudent director and abide by his advice in this matter.

Let us add here two remarks:

(1) Voluntary exterior penances aim at accomplishing three principal effects: first of all, to make satisfaction for past faults; next, to conquer oneself—that is to say, to order our sensible nature so that it will obey our conscience; finally, to seek and obtain a grace that we earnestly desire—for example, deep sorrow for sin or compassion for the pains and sufferings that Christ our Lord endured during his Passion or perhaps for light needed to clarify some question that we are wrestling with. For these reasons exterior penances are closely linked with the prayer of petition.

(2) When the retreatant does not achieve what he desires during the course of the Exercises—for example, the feeling of contrition for his sins—it is often a good idea for him to make some changes in the way he eats, sleeps, or practices penance. Therefore, for two …or three days he should practice some penance and then for two or three days not perform any at all. It is a fact that the spiritual advantages of penances vary with each individual. Another fact is that we often stop doing penance because of our sensuality or because of an inordinate concern for our health. But it can also happen that a person can put too many demands on his body by exaggerating his penances. God our Lord knows our human nature infinitely better than we do, and so in this matter of penances we must experiment in order to find what is proper for each individual.