The way Purgatory has been explained to me it may have more to do with our fleshy desires than the guilt upon our souls. Our sins can be forgiven in this life and yes He does forget them in as much as He welcomes us back home to His side. We are forgiven and our “sins are as far as the east is from the west.” But, are we always interested in going back home? Do we not have hard hearts at least some of the time? Do we not we still desire to sin? Any time we look away from God and choose not His will, but our own, we are culpable or at least vulnerable. I don’t mean to say He can’t help with our hard-heartedness, but that doesn’t necessarily mean He (and we) will finish that work while we’re still walking this Earth.
Understand that when I say “nature” I’m referring to our “fallen” nature, not the nature God gave us. In other words, “God created man in his own image, in the image of God he created him; male and female he created them. … God saw all that he had made, and it was very good.” He created us and it was good, but it was as His children He created us to be. Can a little child survive without his parents or adult guardian? So there you have it, we turned from God and death entered the human experience, but God had a plan. Praise Him for His faithfulness!!
Christopher West, on JP II’s “Theology of the Body” explains it something like this. This is kind of my own paraphrase, except for the scripture verse. Jesus says, “You have heard the commandment not to commit adultery, but the problem is that you desire to commit adultery.” Jesus also tells us He didn’t come into the world to give use more laws, but to fulfill the law; to give us life in the spirit - as opposed to living by the flesh - so that we may not need the law, because we have no desire to break it. Christopher uses this example: You don’t need the commandment ‘Thou shalt not kill" to keep you from killing your wife, because you have no desire to do so.
If you have no desire to sin at all, you are indeed a saint! But even they struggled with temptation and even they committed sin. Yes, we all know how difficult it is to let go of our worldly possessions and ideals, but why is it that we desire to sin? Because we were made to worship. The problem being, if we don’t worship God, we’ll find something else to worship - money, power, esteem, knowledge, sex, self, pop stars, science, the universe, etc, etc, etc…
It must be difficult to let go when Reality opens His arms to receive you into His eternal embrace. Those lesser gods get in the way of our seeing the Truth, but they all must die. When we see the “fullness” of Truth we have no desire to sin. I think it’s good to ask God to help others to see the Light of Truth, so that they may let go of their lesser gods and enter into His glory.