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)

The words translated “it is finished” in the ESV are one word in the Greek, tetelestai (Τετέλεσται for Greek studs).  It is the single most important word in the Scriptures.  Had Jesus not come and died on the cross, then we would still have been in our sins and if we are still in our sins then we will have to pay the penalty for them ourselves (or as a Saturday Night Live skit once put it: We are “screwed, glued, and tattooed”).
My son has Τετέλεσται tattooed on his arm and if I were inclined to get a tattoo, that is what I would get.  It is the mark that I would carry around that says, “When Jesus cried out, “Τετέλεσται,” he meant that cry for me, and I carry on my body a mark that means, “Paid in full.”
The Bible Knowledge Commentary handles this passage well:
“The sixth word or saying that Jesus spoke from the cross was the single Greek work tetelestai which means It is finished. Papyri receipts for taxes have been recovered with the word tetelestai written across them, meaning “paid in full.” This word on Jesus’ lips was significant. When He said, “It is finished” (not “I am finished”), He meant His redemptive work was completed. He had been made sin for people (2 Cor. 5:21) and had suffered the penalty of God’s justice which sin deserved.”