When Jesus had received the sour wine, he said, “It is finished,” and he bowed his head and gave up his spirit.” (John 19:30, ESV)

In the Greek the words “it is finished” are just one word: tetelestai.  The Greek Word of the Day comments about that word:

Among other instances of this word, however, it is finished is the greatest. That statement declares that the goal of redemption had been reached, that salvation by Jesus’ sacrifice was completed. This was the purpose that Jesus Himself spoke of in John 4:34: “My meat is to do the will of him that sent me, and to finish [teleioō] his work” (cf. 17:4; Acts 13:29). This word was actually rooted in ancient culture. As Charles Ryrie writes, “Receipts for taxes found in the papyri have written across them this single Greek word, which means ‘paid in full.’”364 Indeed, Christ paid the full price for our sin. Nothing else either need be paid or could be paid. Salvation is by grace (see Feb. 13–14) alone.

Further, the actual construction in the Greek text (tetelestai) is in the perfect tense, which describes an action that took place in the past with the results of the action continuing into the present. Since it has no direct equivalent in English, it’s often translated as “has,” “have,” or “hath.” Young’s Literal Translation, for example, reads, “It hath been finished.” The significance, then, is clear. While the actual work of Calvary occurred some 2,000 years ago, the results have not diminished one iota through the ages. So, when Jesus uttered those words, It is finished, the work of redemption was accomplished for all time.

John understood well when he used the word tetelestai.  Paid in full, completed, finished, accomplished, done.  God had sent his Son Jesus to do a work and at the cross that work was completed.  Three days later Jesus would prove that he was the Son of God with power when God raised him from the dead. Death could not hold the one who had spoken the word tetelestai.