There is a long standing debate within Protestantism (most especially Calvinism) on when the benefits of Christ's Life and Death are applied to the Elect. This is especially significant in light of the Protestant doctrine of Penal Substitution, which states Christ received the very punishment the elect deserved for their sins. The result of the Atonement, for Protestants, was actual (as opposed to potential) forgiveness. Because Penal Substitution is false and without Scriptural basis (e.g. see here and elsewhere on this blog), some might wonder why I'm talking about this. I think the main benefit of examining this issue is to highlight the fact Protestants can't agree on this key detail, and to suggest they can't agree because the real problem goes deeper, to their view of the Atonement (i.e. Penal Substitution) itself.
The tension that exists in this dispute is very real and causes very real problems, here is the essence of the "problem": if actual forgiveness took place at the cross, then the elect are born forgiven, and thus they don't receive forgiveness at the moment of justification, by faith. That's the primarily logical take on this, which some Protestants accept and is sometimes popularly called "eternal justification". The most common objection to this is primarily on Scriptural grounds, focusing less on the logical implications, pointing to all the passages that speak of the believer's earlier life as unconverted and subjected to sin and God's wrath and such (e.g. Eph 2:1-3), and especially the texts speaking of justification occurring by faith - all of which would make no sense if one was born forgiven.
The latter view is the most common, because most of these Protestants are simply content on having the tension remain, since they've done a far better job than the former camp to harmonize Scripture and logic. The most common formulation is that while the Atonement took place at the Cross, long before we existed, the application of it's effects takes place at the moment the sinner exercises faith and is justified. But the original dilemma is largely unaffected, for if God's justice against the elect's sin was actually satisfied at the Cross - which is exactly what Penal Substitution entails - then God's wrath cannot be upon the elect, ever.
And if this wasn't enough, regardless of which side of these two sides these Protestants take, they are in agreement on another closely related issue, which is that the believer never has to repent of future sins. In other words, if a believer sins any time after his conversion (which most would admit happens), his sin is already forgiven and cannot ever be held against him, and this is the logical consequence of Penal Substitution, because the sin was already punished in Christ at the Cross. But the obvious absurdity that results is that this "conclusion" goes directly against the plain commands of Scripture on repenting whenever one falls into sin (and only the forgiveness of past sins are ever mentioned, e.g. 2 Pt 1:9). The Lord's Prayer, which Jesus taught us (Mat 6), is a classic example: "This, then, is how you should pray: Our Father in heaven ... Forgive us our debts." Protestants realize this difficulty, and while they're forced to admit this repentance is unnecessary before God (since their sins are essentially pre-forgiven), they often try to mask this by claiming this is done for the benefit of the individual's conscience alone (which is still absurd, for they know they won't be held accountable already).
The Catholic can readily see the real problem here, which is in their view on the Atonement. If one's view on the Atonement is wrong, we would indeed expect conflicting "solutions" like these. The fact is, this "tension" isn't really unnecessary, because nobody should be forced to put Scripture and logic - faith and reason - at odds with each other, and as a matter of fact, the Catholic position doesn't believe such is possible.