Tetelestai is the single Greek word behind Jesus' cry from the cross: It is finished. It is a verb of completion — to finish, to accomplish, to bring to its intended end. Far from a groan of defeat, it was a shout of triumph: the work of salvation was fully accomplished, nothing left to add.
In the ancient world, tetelestai was written across a bill to mean paid in full. That is precisely what happened at the cross: the debt of sin that we could never pay was paid completely by Christ. This is why the gospel is good news — salvation is not a project we complete but a finished work we receive. There is nothing left to earn; it is finished.
Tetelestai in Scripture
When Jesus therefore had received the vinegar, he said, It is finished: and he bowed his head, and gave up the ghost.