Yeah, I don't really think of it as in: we need to work to pay it off. More of, when we "pay" for our sins, we are taking the punishment for it we deserve. So I thought maybe he was making reference to the Lake of Fire, and mankind "paying" off their debt (by being punished/corrected and having their sin removed). Maybe that's not what Jesus meant though. xD
I mean, honestly though, is there any form of punishment which is not, in essence, corrective? I know we have the "death penalty" and we have "life in prison," but that only seems to be because A) we cannot always safely correct a person's behavior and B) some people want revenge, and claim it's justice, and C) to get these dangerous people out of innocent peoples' lives. But when a person gets 25 years in prison for man-slaughter (say, because of reckless driving), is not the idea, in part, to correct such behavior for when they get out? I'm sure, if we could fix men's behavior, we'd do that rather than shoving people in prisons.