We have all sinned and we must do penance for our sins, if not now we will do it in the next life. Beyond penance, we must continually mortify ourselves to defend against the temptations of sin.
“To abstain from sinful actions is not sufficient for the fulfillment of God’s law. The very desire of what is forbidden is evil.” - St. Jean-Baptiste de la Salle
“Satisfaction consists in the cutting off of the causes of the sin. Thus, fasting is the proper antidote to lust; prayer to pride, to envy, anger and sloth; alms to covetousness.” - St. Richard of Chichester
"And he said to them: This kind can go out by nothing, but by prayer and fasting." - Mark 9:28
"And there shall be in all the earth, saith the Lord, two parts in it shall be scattered, and shall perish: but the third part shall be left therein. And I will bring the third part through the fire, and will refine them as silver is refined: and I will try them as gold is tried. They shall call on my name, and I will hear them. I will say: Thou art my people: and they shall say: The Lord is my God.." - Zechariah 13:8-9
"Fasting cleanses the soul, raises the mind, subjects one's flesh to the spirit, renders the heart contrite and humble, scatters the clouds of concupiscence, quenches the fire of lust and kindles the true light of chastity." - St Augustine
“Evil is cleansed away by bloody lashes, and a scourging to the inmost being.” - St. Peter Damian
“Without mortification, nothing can be done.” - St. Philip Neri