It may be profitable to dwell for a moment on the advantages of mortification, for such a consideration is calculated to inspire us with more courage and generosity. By mortification we may expiate the temporal punishment due to our sins. We are aware of the fact that though the guilt of sin is remitted by a contrite Confession, there still remains a temporal punishment to be endured. If in the present life we neglect to make atonement, we shall have to suffer in the fire of Purgatory. "Except they do penance for their deeds," says Holy Scripture, "they shall be in a very great tribulation." (Apoc. 2:22). St. Antonine relates that the choice was offered to a sick man (by his guardian angel) either to suffer three days in Purgatory or to remain two years longer on his sickbed. The patient chose the three days in Purgatory. He had hardly been there an hour when he complained to the angel that instead of a few days he had already spent several years in terrible torments. "What is that you say," replied the angel; "your body is still warm on the deathbed, and you speak of years?" If therefore, Christian soul, you have anything to suffer say to yourself: This must be my Purgatory; I shall bear this suffering patiently to atone for my sins, and to gain merit for eternal life."
from The 12 Steps to Holiness and Salvation by St. Alphonsus Liguori