Speak ye comfortably to Jerusalem, and cry unto her, that her warfare is accomplished, that her iniquity is pardoned: for she hath received of the Lord's hand double for all her sins.
In the Bible lands and times when a man owed a debt the elders of the city would post notice of the debt on the city gate. When the debt was paid the elders would fold the notice to cover up the debt and post it back on the gate to show that the man was free of the debt. Jesus Christ paid the price for our sins. God "doubles" the notice, casts our sins behind His back, and remembers them no more. In Christ we have received remission of sins. They are not just covered up, they are completely taken away and forgotten.