The titular question of this blog may sound silly to most people in the pew, but it would be commonplace among Old Testament critical scholars. Late in the 1700s, scholars began to question the unity of the book of Isaiah. It quickly became the norm to argue for two different authors (or groups of authors) in very different time periods.
For example, Isaiah 1-39 is called “First Isaiah.” Critical scholars believe it was written in the 8th century BC in Judah under Assyrian domination. Isaiah 40-66 is called “Second Isaiah” (or sometimes “Deutero-Isaiah”), supposedly written by a different author during or after the Babylonian captivity several centuries later.
It gets worse. Nowadays, it’s common to break the book up further, dividing chapters 40-55 from 56-66 (Second Isaiah and Third or Trito-Isaiah, written in the Babylonian and Persian exiles, respectively). Many different considerations lead to this conclusion, including theological issues, historical issues, and linguistic issues.
However, at its very core, these critical views share the underlying assumptions that anything Isaiah says about the future could not have been written before they happened. In other words, these critical views usually share the presupposition that supernaturalism is not a legitimate explanation for the composition of the Bible. They also have no apparent concern about what this view does to the doctrine of Scripture’s inspiration and inerrancy.
Setting aside any arguments that can be mustered against such a position from a linguistic or historical perspective (and there are many!), Jesus Himself may give the best argument we have for a unity of Isaiah’s book.
In John 12:38-41, John cites two passages from Isaiah – one from Isaiah 53:1 and another from Isaiah 6:10. The first citation comes from so-called “Second Isaiah,” and the first citation comes from “First Isaiah.” But does John or Jesus speak as if the book was originally written in 2-3 stages by more than one author?
Notice John’s language introducing the quote:
“so that the word spoken by the prophet Isaiah might be fulfilled” (12:38 ESV).
John directly attributes the first quote (Isa 53:1) to “the prophet Isaiah.” Not just “Isaiah,” but “the prophet.” And this Isaiah the prophet “spoke” the words that are here quoted. John is not referencing a book, but a person. This is a huge point and will become even clearer as we go.
12:39 introduces the next quote (Isa 6:10), this time only using the word “Isaiah”: “Isaiah said again.” Though the words “the prophet” are not used here again, the word “again” links this individual with the individual mentioned in John 12:38. In other words, the same person who spoke the words quoted from Isaiah 53:1 also spoke the words quoted from Isaiah 6:10! These are one and the same Isaiah!
John 12:41 also solidifies this connection when it says that “Isaiah said these things because he saw his glory and spoke of him.” The first verb here is “said,” which is the same verb (legō) used in 12:38 and 12:39. That we are supposed to understand an actual person is clearly evident by the last half of the verse. This same Isaiah “saw his glory.” This cannot refer to the general writing of a pseudonymous individual “Isaiah” but to an actual person that visibly saw the glory of God!
To summarize, John’s uniform language in 12:38-41 forces a responsible reader to acknowledge that Isaiah was a real person, a prophet, who saw God’s glory and whose words are recorded in both Isaiah 6 and Isaiah 53. If one was to argue, like the critical scholars of the OT, that two different people wrote Isaiah 6 and 53 and lived centuries apart in different historical situations, they would not only have to disregard the clear teachings of the book of Isaiah, but they would have to completely disregard John’s language in John 12!
We can observe a similar argument in Romans 10. Verse 16 cites Isaiah 53 (“Second Isaiah”) and verse 20 cites Isaiah 65 (“Third Isaiah”), yet both are attributed to the same person!
The bottom line is, if we are to take the New Testament at its word, we must understand that Isaiah the prophet was the individual responsible for the words in every part of the book of Isaiah. It’s a simple truth that sometimes profound scholars miss due to their bias against supernaturalism and prophecy.