The following is an excerpt from The MacArthur New Testament Commentary on John 19.

Therefore 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)

Having received the sour wine, Jesus said, “It is finished!” (Gk. tetelestai). Actually, the Lord shouted those words with a loud cry(Matt.27:50;Mark 15:37).It was a shout of triumph; the proclamation of a victor. The work of redemption that the Father had given Him was accomplished: sin was atoned for (Heb. 9:12; 10:12;), and Satan was defeated and rendered powerless (Heb. 2:14; cf.1 Peter 1:18–20; 1 John 3:8).Every requirement of God’s righteous law had been satisfied; God’s holy wrath against sin had been appeased (Rom. 3:25; Heb. 2:17; 1 John 2:2; 4:10); every prophecy had been fulfilled. Christ’s completion of the work of redemption means that nothing needs to be nor can be added to it. Salvation is not a joint effort of God and man, but is entirely a work of God’s grace, appropriated solely by faith (Eph.2:8–9).

His mission accomplished, the time had come for Christ to surrender His life. Therefore, after“ crying out with a loud voice ...‘Father, into Your hands I commit My spirit”(Luke 23:46),He bowed His head and gave up His spirit. Jesus voluntarily chose to surrender His life by a conscious act of His own sovereign will.“No one has taken it away from Me,” He declared,“ but I lay it down on My own initiative. I have authority to lay it down, and I have authority to take it up again. This commandment I received from My Father”(10:18).That He still had the strength to shout loudly shows that He was not physically at the point of death. That He died sooner than was normal for someone who had been crucified (Mark 15:43–45) also shows that He gave up His life of His own will.