Catechism of the Catholic Church 1430-31. Jesus' call to conversion and penance, like that of the prophets before Him, does not aim first at outward works, 'sackcloth and ashes, ' fasting and mortification, but at the CONVERSION OF THE HEART, INTERIOR CONVERSION. Without this, such penances remain sterile and false; however, interior conversion urges expression in visible signs, gestures and works of penance.
Interior repentance is a radical reorientation of our whole life, a return, a conversion to God with all our heart, an end of sin, a turning away from evil, with repugnance toward the evil actions we have committed. At the same time it entails the desire and resolution to change one's life, with hope in God's mercy and trust in the help of His grace.
Act of Contrition
O my God,
I am heartily sorry for having offended Thee,
and I detest all my sins,
because I dread the loss of heaven, and the pains of hell;
but most of all because they offend Thee, my God,
Who are all good and deserving of all my love.
I firmly resolve, with the help of Thy grace,
to confess my sins, to do penance,
and to amend my life.