From the LCMS website:
The doctrine of justification.
Lutherans believe a person is saved by God’s grace alone, through faith alone, in Christ alone. The Roman Catholic Church while at times using similar language, still officially holds that faith, in order to save, must be accompanied by (or “infused with”) some “work” or “love” active within a Christian.
Not infused work but infused
justice, described by the
virtues of faith, hope, and love. These virtues, this justice, is inseparable from the indwelling of the Trinity within the believer, because that indwelling is the
cause of justice in man, the only cause. All of this, while a free gift, is opposed to justice being merely
imputed. Love is the most important virtue as Paul explains in 1 Cor 13, being the very nature of God that He seeks to transform us into. And love
works, for the good of others, by its nature. And God knows when those works are flowing from the right source for the right motivation as per Matt 25:31-46
To put it another way Catholicism teaches that, when a person is justified by God, he's made
genuinely just, because that's God's purpose to begin with, to restore justice/righteousness to His wayward creation; He never made man to be a sinner after all. God allowed man to freely fall, and with His help-
only with His help-man can rise up again. God forgives, and cleanses, and restores man to the heights from which he fell, making him a new creation, but doesn't force man to remain there; He doesn't force us to appreciate the gift that's been given.
But as we
do appreciate it and continue to walk with Him, our justice actually
increases. There's no limit to that potentiality because there's no limit to love, or the righteousness of God. God draws us into greater justice with grace, and the more we're given and the more opportunity we have in life with time, revelation/knowledge, and experience, the more is expected of us. We not only accept the gift, the justification, given, but we confirm and solidify it within ourselves as we participate in achieving it, making our calling and election sure. This is how salvation is worked out with He who works in us. The Parable of the Talents sheds much light on this dynamic.
And in practice, I think a lot of Protestants live as if the above is true, recognizing that what we
do, how we continue to respond throughout our lives, counts.