"After this, Jesus, knowing that all was now finished, said (to fulfill the Scripture), “I thirst.” A jar full of sour wine stood there, so they put a sponge full of the sour wine on a hyssop branch and held it to his mouth. When Jesus had received the sour wine, he said, “It is finished,” and he bowed his head and gave up his spirit." John 19:28-30
It is Finished
When placing the four Gospel texts next to each other, it is quite possible that these were the the last words of the Lord Jesus before he died upon the cross. In the moments leading up to this statement the Bible - itself - gives commentary into the context of this statement: "after this, Jesus, knowing that all was now finished..." (John 19:28). Jesus knew that his mission - his purpose - as to the necessity of his manifestation in the flesh, was complete. In this final crescendo of divine orchestration, an appreciation for what was finished should be acknowledged. In this final moment of Jesus's life, the works of the devil - namely sin - were destroyed.
The Destruction of the Devil's Works
The apostle John later gives additional clarity into the Lord Jesus's mission, in 1 John 3:8 (emphasis added), "Whoever makes a practice of sinning is of the devil, for the devil has been sinning from the beginning. The reason the Son of God appeared was to destroy the works of the devil." Sin was destroyed by Jesus upon the cross - as Paul would also write in Romans - "For God has done what the law, weakened by the flesh, could not do. By sending his own Son in the likeness of sinful flesh and for sin, he condemned sin in the flesh, in order that the righteous requirement of the law might be fulfilled in us, who walk not according to the flesh but according to the Spirit." Romans 8:3-4. Thus, Jesus being manifest in the likeness of sinful flesh, put to death sin upon the cross. Every nail in Him, was a nail being hammered into the likeness of sinful flesh - though Jesus himself had never transgressed the law, and so - never having sinned. Jesus - the Lamb of God - was a worthy sacrifice because of His sinless nature, as Peter would write of the immeasurable worthiness of Jesus, "knowing that you were ransomed from the futile ways inherited from your forefathers, not with perishable things such as silver or gold, but with the precious blood of Christ, like that of a lamb without blemish or spot. (1 Peter 1:18-19 - emphasis added). Jesus's life on earth was a record of perfection, and therefore he is a worthy substitute for all of humanity.
Jesus Fulfilled the Law
“Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them. For truly, I say to you, until heaven and earth pass away, not an iota, not a dot, will pass from the Law until all is accomplished." Matthew 5:17-18.
We've established that Jesus came to destroy the works of the devil, namely, sin. The mechanism which Jesus was able to do this was by becoming subject to the Law, and so fulfilling the Law - proving his worthiness as a sacrifice for the propitiation for the sin of the world, in his death upon the cross. As Millard Erickson writes,
"He was born under the law. He who had originated the law and was the Lord of it became subject to the law, fulfilling all of it. it was as if an official, having enacted a statute that those under him had to follow, himself stepped down to a lower position where he too had to obey. Jesus's becoming subject to the law was complete. Thus he was circumcised at the age of eight days, and at the proper time he was brought to the temple for the rite of the mother's purification. By becoming subject to the law, says Paul, Jesus was able to redeem those who are under the law. (Galatians 4:5)"
Synthesis
Thus, in Jesus's fulfillment of the Law, Jesus overcame the desires of the flesh to sin. In His final moments, he said "It is finished," before giving up His spirit. The context of this phrase is not merely the acknowledgement of a single prophecy fulfilled, but is loaded with meaning, which includes his acknowledgment of His mission to destroy the works of the devil, namely sin - by his righteousness - evidenced by his fulfilling of the Law, that through His death on the cross, the righteous requirement of the law would be fulfilled in those who would place their faith in His substitutionary atonement upon the cross. As the MacArthur Commentary Bible points out about John 19:30,
"The verb here carries the idea of fulfilling one's mission and religious obligations (17:4). The entire work of redemption had been brought to completion. The single greek word here (translated "it is finished") has been found in the papyri being placed on receipts for taxes meaning "paid in full."
Jesus, being subject to the Law, never transgressed the law - and so fulfilling the Law - through his approximately 33 years of life, and was therefore the only one who could pay for the sins of the world, in full. When Jesus died upon the cross, the works of the devil - namely, sin - were "finished."
Grace and peace,
Eleazar