While every sin is forgiven, there are also times when we are to pay restitution to those we have done something to. The payment is owed to the one whom damage is done. Sometimes you damage more than one person, you pay to all the people you have damaged. When it comes to damages against God, all restitution is already paid. The girl who drove into your fence owes you for a fence, regardless of how sorry she is, and you, being the magnanimous person you are, could forgive her of all damages. If, however, her brother came to you and said “My sister is learning to drive, and she might hit your fence, here is enough money to cover any damages she might do.” then you should not expect any more payment. In other words, she is ALREADY forgiven.
So we'd say that When I sin, I , in principle, owe a debt to God. But we say "in principle" because it's paid. But I may also owe a debt to someone else, and THAT debt is not paid by the atonement wrought in Christ.
Oh wait! In a way it is. If I forgive the debt, then I am paid by Christ. Isn't that somehow right?
It's interesting, and I'm wanting to pick my way carefully, because of ψ 51 v. 6 "against you only have I sinned .." And that seems really true at a deep level. All sins are against God and all debts are somehow owed to Him. And thanks be to God who has in Christ squared the account.
I think where my mind wonders next is to wonder, as I have been doing for about 11 months or so, if accounting is an adequate analogy for justice.