> They need suffer only a moment's guilt, before proceeding fearlessly back into the world.

Well, maybe not. Dostoevsky was Orthodox, so I don't know how he would think about this...

From a Catholic perspective sin has both temporal and eternal consequences. God can forgive a truly repentant person any sin, ordinarily through the ministry of the Church by the power and authority of Christ, establishing or returning a person to the life of divine grace in their soul, but the temporal consequences of their sin/s may remain to be repaired.

By analogy, suppose my neighbor became unreasonably angry with me, becoming so incensed that he threw a rock at one of my windows causing it to shatter. Then, after a day of cooling off, he apologized and asked forgiveness. Now suppose I granted him forgiveness, moved by his sincerity and a mutual desire to repair the relationship. The shattered window remains — the glass needs to be cleaned up, and a new window must be purchased and installed. Maybe my neighbor has the resources and skill to do the repair himself; or maybe he can pay directly or reimburse me for contract labor; or maybe he can't afford the repair but promises to pay me back; or maybe one of his family members pays me instead. One way or another, the window will be repaired and my neighbor bears responsibility for it.

So sin, generally, is like this, from the Catholic POV. If the forgiven sinner is not able to make repair before their life ends, then they will suffer in purgatory after death before enjoying the beatific vision. The purification will be more severe depending on the number and gravity of sins. Some mystics claim to have been informed about souls that will suffer in purgatory flames hotter than those of damnation until the last moment before the general judgment, so terrible were their sins and unrepaired consequences of the same.