What is the absolute, number one, obsession among post-reformation Christians: Justification. Why this obsession, if they feel that Jesus did it all and they are already home free? The protestant world is absolutely OCD-level obsessed with justification. Pastors preach incessantly about it - even to the converted. This seems nonsensical if Jesus already paid the entire price. Denomination debates denomination over justification, have for 500 years, and will do so until the end of time. Many teach that sin has no effect on salvation!
Catholics have no such burden. We know that faith is required, of course, but we have the Sacraments as instituted by Christ. Our sins are gone and once penance is complete, our temporal punishment due to sin is also gone. Yet, due to our concupiscence, we are inclined to sin again - to do the wrong thing. From this, and from knowledge that sin separates us from God, we feel the guilt. Without guilt, what else would motivate us to improve in the virtues? To self-control?
The reformation’s heresy, among many others, is that they place little to no importance on thoughts or behavior - only on what they believe. “Faith alone!!!” This is 100% against what our Lord taught, i.e. “He who lusts after a woman has committed adultery with her in his heart.” Why would Jesus say this if sin had no price? Why didn’t He say “Don’t worry! I’ll pay the price for you!”?
He opened the gates of heaven, but He does not carry us through them. Sin is real. Sin is the only thing that separates us form God. You want to feel much better right now with absolutely no effort? Re-define sin as destroyed in the past and as having no effect on us today. Easy, but self-delusion does not give a pass through the gates of heaven.