From chapters 1-39 and chapters 40-66, there is an immense change of subject from these two "halves". 1-39 are more pronouncements of destruction to Judah and surrounding evil nations, while 40-66 are reassurances of restoration. (Isaiah 34:5-8, contrast Isaiah 55:12-13) Furthermore, certain phrases that are nearly unique to Isaiah are a good indication of the oneness of the two "halves". For example, the term "the Holy One of Israel" is found 12 times in chapters 1-39 and 13 times in 40-66. Throughout the rest of the Bible, that phrase is found only 6 times!-Isaiah 12:6; 54:5
Another indication of the book having been written by one author is the fact that Jesus Christ and the Apostle Paul quoted from all parts of the book of Isaiah and accredited the one man. Obviously, Jesus would have been aware if Isaiah had been written by two different people.
Why, though, do critics make this charge and why are the so adamant about it? Because, if it is true that Isaiah wrote the entire book, it presents problems. You see, the book of Isaiah makes a startling prophecy which is very detailed and very accurate. And the prophecy was written nearly 200 years in advance!
"[Jehovah], the One making the word of his servant come true, and the One that carries out completely the counsel of his own messengers; the One saying of Jerusalem, 'She will be inhabited,' and of the cities of Judah, 'They will be rebuilt, and her desolated places I shall raise up'; the One saying to the watery deep, 'Be evaporated; and all your rivers I shall dry up'; the One saying of Cyrus, 'He is my shepherd, and all that I delight in he will completely carry out'; even in my saying of Jerusalem, 'She will be rebuilt,' and of the temple, 'You will have your foundation laid.'
"This is what Jehovah has said to his anointed one, to Cyrus, whose right hand I have taken hold of, to subdue before him nations, so that I may ungird even the hips of kings; to open before him the two-leaved doors, so that even the gates will not be shut: 'Before you I myself shall go, and the swells of land I shall straighten out. The copper doors I shall break in pieces, and the iron bars I shall cut down.'"-Isaiah 44:26-45:2
This prophecy is of interest because it foretells--in great, accurate detail--the fall of Babylon and the restoration of Jerusalem. It even names the man who is to accomplish this--Cyrus. Did this prophecy come true?
Two hundred years after Isaiah, the Jews were in captivity in Babylon. One night, while a wild party was going on, the gates of Babylon were left open. Then a man, Cyrus the Great, diverted the water of the Euphrates River, making the protective water moat drain until Cyrus and his armies could cross on foot. This army walked right through the open gates of Babylon and took the city, virtually without a fight. Then, this new world power, the Medo-Persian world power, allowed all of the captives to return home, including the Jews. They even gave a command saying that the temple should be rebuilt. All of this happened as Isaiah foretold.
Now, in the book of Isaiah, yet another prophecy is awaiting fulfillment.
"And the wolf will actually reside for a while with the male lamb, and with the kid the leopard itself will lie down, and the calf and the maned young lion and the well-fed animal all together; and a mere little boy will be leader over them. And the cow and the bear themselves will feed; together their young ones will lie down. And even the lion will eat straw just like the bull. And the sucking child will certainly play upon the hole of the cobra; and upon the light aperture of a poisonous snake will a weaned child actually put his own hand. They will not do any harm or cause any ruin in all my holy mountain; because the earth will certainly be filled with the knowledge of Jehovah as the waters are covering the very sea."-Isaiah 11:6-9This is one of the first detailed prophecies about a coming paradise earth in the Bible.
In the second part of Isaiah, another prophecy regarding the same thing is uttered.
"Therefore this is what the Sovereign Lord Jehovah has said: 'Look! My own servants will eat, but you yourselves will go hungry. Look! My own servants will drink, but you yourselves will go thirsty. Look! My own servants will rejoice, but you yourselves will suffer shame. Look! My own servants will cry out joyfully because of the good condition of the heart, but you yourselves will make outcries because of the pain of heart and you will howl because of sheer breakdown of spirit...For here I am creating new heavens and a new earth; and the former things will not be called to mind, neither will they come up into the heart. But exult, you people, and be joyful forever in what I am creating. For here I am creating Jerusalem a cause for joyfulness and her people a cause for exultation. And I will be joyful in Jerusalem and exult in my people; and no more will there be heard in her the sound of weeping or the sound of a plaintive cry.'
"'No more will there come to be a suckling a few days old from that place, neither an old man that does not fulfill his days; And they will certainly build houses and have occupancy; and they will certainly plant vineyards and eat their fruitage. They will not build and someone else have occupancy; they will not plant and someone else do the eating. For like the days of a tree will the days of my people be; and the work of their own hands my chosen ones will use to the full. They will not toil for nothing, nor will they bring to birth for disturbance; because they are the offspring made up of the blessed ones of Jehovah, and their descendants with them. And it will actually occur that before they call out I myself shall answer; while they are yet speaking, I myself shall hear.'"-Isaiah 65:13-24
Yes, our God, Jehovah, has promised an earthly paradise where all men will live in peace under the reign of Jesus Christ. He used His holy spirit to inspire Isaiah to write these things. He used the same Isaiah to write the first and second half of this book. The harmony throughout the book testifies to this. People who want to discredit the great prophecy mentioned at in Isaiah 44-45 will use any means necessary to make it seem unauthentic. However, we, with a little study and meditation, can surely see the hand of Jehovah on the same man--Isaiah!