...before He died, Jesus cried, ―It is finished‖ (John 19:30). These three English words translate one Greek word: tetelestai (teh-TELL-ess-tie). With this marvelous word, Christ says, "It stands accomplished." Everything that needed to be done has been done; every bit of the mission the Father gave Him for His glory, the redemption of His people, the defeat of Satan, and the reclamation of the planet, has been brought to completion.
Jesus is saying that everything necessary for the completion of God‘s saving plan has been accomplished. At that moment, the great curtain that separated the Holy Place from the Most Holy Place tore in two, from top to bottom (Matt. 27:51; these compartments were discussed in chapter 4). This was an act of God, trumpeting that the way into the Holiest Place had been thrown open by the sacrifice of Jesus (cf. Heb. 9:8; 10:19–20).
The reality that all the sacrifices had foreshadowed throughout the many centuries of OT history now had come to fulfillment. The picture gave way to the reality, the shadow to the body, the promissory note to the full payment. God‘s very presence was open to sinful man through the substitutionary atoning death of the Son of God.
(from The World-Tilting Gospel, 128)