"And one of them, Caiaphas, being high priest that year, said to them, 'You know nothing at all, nor do you consider that it is expedient for us that one man should die for the people, and not that the whole nation should perish.' Now this he did not say on his own authority; but being high priest that year he prophesied that Jesus would die for the nation, and not for that nation only, but also that He would gather together in one the children of God who were scattered abroad. Then, from that day on, they plotted to put Him to death. Therefore Jesus no longer walked openly among the Jews, but went from there into the country near the wilderness, to a city called Ephraim, and there remained with His disciples."
The position of high priest was not transferred from year to year. The wording in John 11:49 simply indicates that this man was high priest the year that Jesus was "tried" and crucified.
Caiaphas begins with a stinging rebuke - "You know nothing at all." He then proceeds to explain what must be done.
"It is expedient for us that one man should die for the people, and not that the whole nation should perish" - Whether or not they really believed Jesus to be a threat to the nation didn't matter, for they would portray Him as such and come to the conclusion that He must be put to death for the safety of the nation! Caiaphas was more concerned about what was expedient rather than what was just. Tragically, they only consider two options here, but there is a third: Believe in Jesus and save the nation both politically and spiritually! However, this would require them voluntarily giving up their influence and power. This they simply would not do.
"He did not say this on his own" (John 11:51). The writer, John, is informing us that there is more to the words here than the meaning which Caiaphas had intended. By the will of God this high priest "prophesied that Jesus would die for the nation." What Caiaphas simply meant was that Jesus must be killed in order to spare the nation. But, it is now easy to see the deeper significance in the words that God influenced him to speak. Jesus not only died for the Jewish nation but for all the world (cf. I John 2:2). Caiaphas was merely speaking as a cold-blooded murderer, but his words were also the right ones to express the glorious truth regarding God's redemptive love! Without becoming aware of it, the villain had become a true prophet!
Caiaphas continued speaking in John 11:52 - "Also that He would gather together in one the children of God who were scattered abroad." Caiaphas evidently believed that Jesus' death would unite the Jewish people, even those in far away places. In a spiritual sense, this is exactly what did happen for those who obeyed the gospel, the true children of God (cf. Eph. 2:13-16; Gal. 3:28).
Although it is uncommon for one who is working against God's will to prophesy for Him, it is not unheard of (e.g., Balaam in Num. 22ff and Saul in I Sam. 19:20-24).
"Then, from that day on, they plotted to put Him to death" (John 11:53). It wasn't too difficult to convince them to do what they already desired. They had condemned Jesus without a hearing and they would seek His death unjustly. They tried to quiet their consciences by claiming to see political dangers in allowing Jesus to live. They would claim to kill Jesus for the welfare of the public, when in truth they would kill Him out of hatred and envy.
"Jesus no longer walked openly among the Jews" - He remained out of the public view until shortly before the Passover because of their extreme antagonism.