Holy Mother Church teaches that conversion and penance does not aim first at outward works, but at conversion of the heart. This interior conversion leads to its expression in visible signs, but without the interior conversion, these outward penances remain fruitless.

The end of penance is not suffering for the sake of suffering. Penance is a reparation for our failings and a tool by which we clear away the unnecessary clutter in our lives to make room for Christ.

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St Thérèse of Lisieux teaches us by example:

I understood that to become a saint one had to suffer much, seek out always the most perfect thing to do, and forget self. I understood, too, that there are many degrees of perfection and each soul was free to respond to the advances of Our Lord, to do little or much for Him, in a word, to choose among the sacrifices He was asking. Then, as in the days of my childhood, I cried out: ‘My God I choose all!’ I do not want to be a saint by halves, I’m not afraid to suffer for You, I fear only one thing: to keep my own will; so take it, for I choose all that You will!

…When we unite our sufferings to Christ, no matter how small, we take up our cross as Christ tells us, and we follow in his footsteps.

—Br Jacob Bertrand Janczyk, OP, The Key to Holiness: An Annoying Co-Worker?