For those who want to understand why the divide between RCC and Protestantism, here is a significant article by RC Sproul.
Rome set forth their doctrine -- and still does -- that God will never declare a person just until that person actually, under divine scrutiny, is found to be just...when God looks at us, he will not say that we are just until he sees that we really are just.
Rome teaches that we cannot be just without grace, that we will never become just without faith, and that we will never become just without the assistance of Christ. We need faith, we need grace, and we need Jesus. We need the righteousness of Christ infused or poured into our soul, but you must cooperate with that grace to such a degree that we will in fact become righteous. If we die with any impurity in our soul, thereby lacking complete righteousness, we will not go to heaven. If no mortal sin is present in our life, we will go to purgatory, which is the place of purging. The point of the purging is to get rid of the dross so that we become completely pure. It may take three years or three million years, but the object of purgatory is to make us righteous so that we can be admitted into God's heaven.
Part of the reason for this belief, that justification is rooted in an inherent righteousness in the sinner, comes from something unfortunate in church history. In the early centuries, when the Greek language passed away from the central attention of the church fathers and Latin became the dominant language, many scholars read only the Latin Bible, not the Greek bible, and they borrowed the Roman or Latin word for justification, iustificare, from which we get the English work justification. The Latin verb ficare means "to make" or "to shape" or "to do." Isutus means "righteousness" or "justice," so iustificare literally means "to make righteous," which we believe is what happens in sanctification, not in justification.
The Greek word that we are dealing with here in the Romans text is the word dikaioo, dikaiosune, which does not mean "to make righteous" but rather "to declare righteous." In the Roman Catholic view, God will never pronounce a person just or righteous until, by the help of God's grace and Christ, that person actually becomes righteous. [But] If God were to judge us tonight, what would he find? Would he find sin in our lives? Could he possibly declare us just if he considers only the righteousness that he finds in us today? Remember what the Apostle Paul said: "By the deeds of the law no flesh will be justified in His sight" (3:20). That is precisely why the ground for our justification cannot be found in us or in any righteousness inherent in our souls. That is why we need so desperately what Luther called a iustia alienum, an alien righteousness, a righteousness that comes from outside ourselves. Luther called this righteousness extranos, outside or apart from us.
In simple terms, this means that the only righteousness sufficient for us to stand before the judgment of God is the righteousness of Christ.
Excerpt from Romans (St. Andrew's Expositional Commentary) by R.C. Sproul