As a Reformed (Presbyterian) Protestant who greatly admires the Catholic Church, I have been working on how to tease out the difference between the two views of justification. They have long seemed to be more similar than different - perhaps nothing more than different perspectives on the same truth.
Both Catholics and Protestants believe we are justified by grace through faith. Both Catholics and Protestants believe that saving faith definitely produces obedience and good works, and that saving faith is not spurious, but persevering. Both Catholics and Protestants believe that the basis for justification is not works done by us, but rather Christ’s death on the cross where He satisfied God’s demands for justice.
So what are the differences? The main difference is that Catholics believe that we can lose our state of justification through mortal sins, while (most) Protestants believe that we cannot lose our state of justification, though we can fall out of God’s favor through sin. I believe this is due to a misunderstanding of justification by both Protestants and Catholics.
Justification is a legal term that God will use to declare all true believers righteous at the last judgment (Romans 2). Any status of being justified we have now is merely the position we are in before God - it is the guarantee of the future reality. That guarantee is sealed by the indwelling of the Holy Spirit, Who sanctifies us and produces obedience and good works (Ephesians 1:13-14).
Protestants err by confusing justification with conversion. Too many Protestants believe that when a person fully commits their life to Christ they are immediately and irrevocably justified at that moment. But this is not even true in classical Reformed theology! Nowhere does the Bible say that justification occurs when one outwardly converts to Christianity. A true believer can be assured of their justification, but justification ultimately occurs at the last judgment. We can be given the promise of that future reality, but no one is truly and finally justified the moment they are converted or even baptized.
And that leads me to the Catholic error. Catholics believe that grace is infused at the time of baptism, and this renders us justified before God. This justification can be lost, however, through mortal sin, and only through repentance can that right standing with God be regained. This might be true in the sense that someone might be baptized who does not have true saving faith, but it is not true that we can be in and out of a position of justification, as Jesus Himself makes clear in John 10, and which both Peter and Paul re-iterate in the New Testament. Catholics might say that mortal sin requires confession and repentance to return to a position of justification, but I believe the flip side is true: those who are justified and have true saving faith will invariably confess and repent of their mortal sins. Catholics believe that we confess to RETURN to a state of justification, when in reality we confess BECAUSE we are in a state of justification and are continually being sanctified.
A Catholic objection to this might be that someone might turn their back on God and live a life of sin, and thus lose their justification. I would argue that such a person was never truly justified to begin with, however sincere their faith appeared to be, because saving faith is by definition persevering faith (Hebrews 6:11-12).
I think these two views can be reconciled through the right view of justification. Justification comes through true saving faith in Jesus Christ, but saving faith produces good works and obedience (i.e. Charity), which includes continual confession and repentance of sins. Saving faith is also persevering, meaning it is not simply a “one and done” prayer or baptism. Thus a true believer will constantly confess and repent: they don’t lose their justification, but neither should they consider themselves justified because they “asked Jesus into their heart” at some point in their life (a common Protestant error). A true believer will remain justified as Protestants teach, but a true believer will invariably be obedient (which includes confession and repentance) and produce good works as Catholics teach.
So I believe if Protestants and Catholics shift their perspective on justification slightly they can retain their historic teaching and be reconciled, at least as far as this doctrine goes. Any thoughts and critiques would be greatly appreciated!