The word τετέλεσται- the sixth of Christ's Seven Last Words from the Cross- is usually translated "It is finished." But it has a much deeper meaning than that.
In the ancient world, it was the word that would be written across a canceled bill. "Tετέλεσται" meant "paid in full."
Jesus actually spoke Aramaic, of course, But the word τετέλεσται- the word the Holy Spirit uses in Scripture to express His thought- conveys far more than meets the eye. It conveys the most essential thing about Christ's suffering and death: its completeness, not merely as satisfaction to His Father's justice for every sin you have ever committed or ever will ever commit, but its having left nothing undone. Even your repentance and faith are His doing in you through the Word, and not your own contribution needed somehow to complete some unfinished business left over from Golgotha.
It's not just that Jesus has already paid for your sin. It's that you don't have to look to the quality of your own repentance, or of your faith, or anything else of your own for assurance of God's constant love and forgiveness. All you have to do is to look precisely away from yourself and your own supposed contributions to forgiveness, to Jesus.
Tετέλεσται. "Paid in full." There is nothing else for you to do or worry about doing. Your sin cannot hurt you as long as you look away from your own efforts and merits, to Jesus. He has done it all. Tετέλεσται. It is finished. Paid in full!