Jesus drinks the sour wine for the aforementioned reasons. It is interesting to note that when He was offered wine mixed with numbing drugs (Matt 27:34, Mark 15:23), He refused it because He wanted to go through His sufferings with a clear mind.

Matthew 27:34  There they offered Jesus wine to drink, mixed with gall; but after tasting it, he refused to drink it.

Mark 15:23  Then they offered him wine mixed with myrrh, but he did not take it.

Upon receiving the drink, Jesus says “It is finished,” which is one word (tetelestai) in the Greek. But He doesn’t just say it, He shouts it as is described in (Matt 27:48-50, Mark 15:36-37) which do not give the words spoken but do come immediately after He received His drink. This is not a moan of a defeated person, but the cry of a Victor! cf. (John 16:33, Rev 5:5) He knew that He was going to die and He knew exactly why (Matt 20:28, 26:28). The purpose of His life on earth was to do the will of the Father (John 4:34) and now that will had been totally accomplished (Act 2:23)! Jesus had finished the work the Father had entrusted to Him. Corell sees tetelestai as the key word of the gospel of John and I tend to agree with him. Anton Baumstark says that for John “even the Resurrection could add nothing to the remembrance of that triumphant cry” (Comparative Liturgy, London, 1958, p. 106).

Matthew 27:48-50  Immediately one of them ran and got a sponge. He filled it with wine vinegar, put it on a stick, and offered it to Jesus to drink.
  The rest said, “Now leave him alone. Let’s see if Elijah comes to save him.”  And when Jesus had cried out again in a loud voice, he gave up his spirit.

Mark 15:36-37  One man ran, filled a sponge with wine vinegar, put it on a stick, and offered it to Jesus to drink. “Now leave him alone. Let’s see if Elijah comes to take him down,” he said.  With a loud cry, Jesus breathed his last.

John 16:33  “I have told you these things, so that in me you may have peace. In this world you will have trouble. But take heart! I have overcome the world.”

Revelation 5:5  Then one of the elders said to me, “Do not weep! See, the Lion of the tribe of Judah, the Root of David, has triumphed. He is able to open the scroll and its seven seals.”

Matthew 20:28  just as the Son of Man did not come to be served, but to serve, and to give his life as a ransom for many.”

Matthew 26:28  This is my blood of the covenant, which is poured out for many for the forgiveness of sins.

John 4:34  “My food,” said Jesus, “is to do the will of him who sent me and to finish his work.

Acts 2:23  This man was handed over to you by God’s set purpose and foreknowledge; and you, with the help of wicked men, put him to death by nailing him to the cross.

It was not just the work of Christ on earth doing the will of the Father that was finished on the cross that day, but many things: the types and prophecies of the suffering Christ; the partition between Jews and Gentiles (Eph 2:14-15); sin (Dan 9:24, Heb 9:26); His sufferings on the cross (Heb 12:2); His life (John 17:11, 2 Tim 4:7) (like Paul’s); and the redemption and salvation of man. All of these things were completed by the substitutionary death of God’s Messiah.

Ephesians 2:14-15  For he himself is our peace, who has made the two one and has destroyed the barrier, the dividing wall of hostility,  by abolishing in his flesh the law with its commandments and regulations. His purpose was to create in himself one new man out of the two, thus making peace,

Daniel 9:24  “Seventy ‘sevens’ are decreed for your people and your holy city to finish transgression, to put an end to sin, to atone for wickedness, to bring in everlasting righteousness, to seal up vision and prophecy and to anoint the most holy.

Hebrews 9:26  Then Christ would have had to suffer many times since the creation of the world. But now he has appeared once for all at the end of the ages to do away with sin by the sacrifice of himself.

Hebrews 12:2  Let us fix our eyes on Jesus, the author and perfecter of our faith, who for the joy set before him endured the cross, scorning its shame, and sat down at the right hand of the throne of God.

John 17:11  I will remain in the world no longer, but they are still in the world, and I am coming to you. Holy Father, protect them by the power of your name—the name you gave me—so that they may be one as we are one.

2 Timothy 4:7  I have fought the good fight, I have finished the race, I have kept the faith.

Jesus then “bowed His head”. This is the same expression as found in (Matt 8:20) where it is used for going to bed. This is a peaceful thought, totally unlike the death produced by the circumstances through which He is going should produce. Morris notes that, “That resting place for His head which He did not have on earth He found on the cross.” Origen of Alexandria beautifully observed that Jesus “bent the head and took His departure in the act of resting it, as it were, on the lap of the Father, who could cherish it and strengthen it in His bosom.”

Matthew 8:20  Jesus replied, “Foxes have holes and birds of the air have nests, but the Son of Man has nowhere to lay his head.”

The bowing of His head may have additional meaning. It is an indication of His total submission to the will of the Father, and it could be symptomatic of the weight of our sins which He was bearing. Note how the psalmist’s sins affected him as recorded in (Psa 38:4, 40:12).

Psalms 38:4  My guilt has overwhelmed me like a burden too heavy to bear.

Psalms 40:12  For troubles without number surround me; my sins have overtaken me, and I cannot see. They are more than the hairs of my head, and my heart fails within me.

Jesus then “gave up His spirit” which is certainly not the usual way of referring to death, but then the relation of Jesus to death was unlike anyone else’s. This expression is quite similar to that found in (Isa 53:12) and is indicative of a voluntary action. It is almost strong enough to be translated as He “dismissed His spirit.”

Isaiah 53:12  Therefore I will give him a portion among the great, and he will divide the spoils with the strong, because he poured out his life unto death, and was numbered with the transgressors. For he bore the sin of many, and made intercession for the transgressors.

Immediately after this the veil in the Temple separating the Holy Place from the Holy of Holies was torn in two from top to bottom and many other miraculous things took place. These are recorded in (Matt 27:50-54, Luke 23:44-46).

Matthew 27:50-54  And when Jesus had cried out again in a loud voice, he gave up his spirit.  At that moment the curtain of the temple was torn in two from top to bottom. The earth shook and the rocks split.  The tombs broke open and the bodies of many holy people who had died were raised to life.
  They came out of the tombs, and after Jesus’ resurrection they went into the holy city and appeared to many people.  When the centurion and those with him who were guarding Jesus saw the earthquake and all that had happened, they were terrified, and exclaimed, “Surely he was the Son of God!”

Luke 23:44-46  It was now about the sixth hour, and darkness came over the whole land until the ninth hour,  for the sun stopped shining. And the curtain of the temple was torn in two.  Jesus called out with a loud voice, “Father, into your hands I commit my spirit.” When he had said this, he breathed his last.

What is the significance of the torn veil? We now have access to God. 

Hebrews 10:19-20  Therefore, brothers, since we have confidence to enter the Most Holy Place by the blood of Jesus,  by a new and living way opened for us through the curtain, that is, his body,

What is the significance that it was torn from the top to the bottom? It was an action of God and not of man.