"The principle reason for performing exterior penance is to secure three effects:
1. To make satisfaction for past sins;
2. To overcome oneself, that is, to make our sensual nature obey reason, and to bring all of our lower faculties into greater subjection to the higher;
3. To obtain some grace or gift that one earnestly desires. Thus it may be that one wants a deep sorrow for sin, or tears, either because of his sins or because of the pains and sufferigns of Christ our Lord; or he may want the solution of some doubt that is in his mind." -- St. Ignatius Loyola, Spiritual Exercises.