As Catholics, we believe that God forgives us the guilt of sin because of Christ’s sacrifice on the cross, but we still need to deal with sin’s “temporal consequences” one way or the other (i.e., in this life through practicing penance, in the next life through purification in Purgatory, or through some combination of the two).  I first learned about this concept at Fuller Theological Seminary in Early Church History with Dr. Nathan Feldmeth (fall 2003).  I have found the distinction between guilt and temporal consequences hard to understand, so I was glad to read a helpful explanation of the distinction in Dr. Paul Thigpen’s Lenten article entitled “Why Practice Penance?”  (March 2011 Newsletter of the Coming Home Network International.  Pages 10-11..)  Here is an excerpt with a helpful analogy:

Suppose you tell your five-year-old that he can’t jump off a tall fence because he will hurt himself.  But he does it anyway and breaks his arm.  When he calls out to you crying in pain, he’s quite remorseful for his misbehavior and afraid that your anger will alienate you from him.

At this point, you forgive him for disobeying you–that is, you lay aside your anger at his wrongdoing so that it doesn’t stand between the two of you.  But other consequences of his sin must still be dealt with.  You must take him to the hospital to have his broken arm set, and that will be a painful process.

The truth is that we’ve all disobeyed God and broken some of our spiritual “bones.”  God forgives us of the guilt resulting from our sin, the break in our relationship with Him.  He restores the friendship.  But He doesn’t wave a magic wand, bypassing our free will, to fix those “bones.”

Instead, we must undergo a process that undoes what we have done, and it requires our cooperation.  We must work, with the assistance of divine grace, to let go of whatever binds us, straighten out whatever is crooked within us, repair what is broken, restore what we have unlawfully taken, embrace whatever truths we have denied, and learn to love God above all things.  That process is what we call penance.