I read something interesting in the YouCat Youth Catechism today. It was a clarifying way to describe Purgatory. On "Question 159: What is Purgatory?" This is the response:
When Peter had betrayed Jesus, the Lord turned around and looked at Peter: “And Peter went out and wept bitterly”—a feeling like being in purgatory. Just such a purgatory probably awaits most of us at the moment of our death: the Lord looks at us full of love—and we experience burning shame and painful remorse over our wicked or “merely” unloving behavior. Only after this purifying pain will we be capable of meeting his loving gaze in untroubled heavenly joy.
Suddenly Purgatory makes even more sense. When we die and meet God face to face, and are assailed by God's infinite love, we will suddenly become acutely aware of our iniquities, how we have failed him. We will see ourselves for what we are as sinners. The floodlights will come on.
And because God is perfect love and we long to be with him, we will feel ashamed. This pain is what will purify us. This rightful shame will melt away the stains of our sins, just as a fire purifies silver of all its stains until it shimmers perfectly.
If we did not feel this shame over our past sins that have stained our soul, then we could not enter heaven. If we did not have our sins purified, we could not enter. After all "Nothing unclean will enter it" (Rev 21:27). God grants us forgiveness because of his Son's sacrifice and because we ask for it but, as with any wrongdoing in the world, even after we ask and are granted forgiveness, the results of that sin remain until we repay the wrongdoing. If I break my sister's toy, I can tell her I am sorry and she can forgive me, but the consequence of that sin, a broken toy, is still present until I reconcile with her by repairing it or purchasing a new one.
And so, when Peter sinned by denying Christ, he had to repent. He had to cry and feel the pain of remorse because he knew the shame of what he had done. He suffered, his own purgatory, and thus he was healed.
Our own Purgatory will likely be painful, though it is a sure sign that we will reach Heaven. It will be painful because we will feel so utterly remorseful in the sight of God. Remorseful, because we love him. ("Yes, Lord, you know that I love you." (John 21:15) ) But, in that moment, we will know perfectly God's love for us, and we will feel love for him as greatly as God intended.